Note: Descriptions are shown in the official language in which they were submitted.
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1 338237
A PROCESS FOR THE DIRECT PRODUCTION OF ALKYL GLYCOSIDES
Background of the Invention
The invention is a process for the direct production
of surface-active alkyl glycosides, i.e. the acetals of
sugars and aliphatic alcohols, by direct acid-catalyzed
reaction of the alcohol with the saccharide with
elimination of water.
Field of the Invention
The name alkyl glycosides as used herein refers to the
reaction products of saccharides and aliphatic alcohols,
the saccharide component being selected from any of the
aldoses or ketoses in the broadest sense hereinafter
referred to as glycoses, including for example glucose,
fructose, mannose, galactose, talose, gulose, allose,
altrose, idose, arabinose, xylose, lyxose and ribose. The
aldoses are preferably used by virtue of their better
reactivity. Among the aldoses, glucose is particularly
suitable because it is readily obtainable and available in
industrial quantities.
The alkyl glycosides produced with particular
preference by the process according to the invention are
the alkyl glucosides. The term alkyl as used herein
includes the residue of an aliphatic alcohol of any chain
length, preferably a primary aliphatic alcohol and, more
preferably, a fatty alcohol obtainable from natural fats.
1 338237
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The term encompasses saturated and unsaturated residues and
mixtures thereof, including those of different chain length
in admixture. The names alkyl oligoglycoside, alkyl
polyglycoside, alkyl oligosaccharide and alkyl
polysaccharide apply to those alkylated glycoses in which
an alkyl radical in the form of the acetyl, is attached to
a residue comprising more than one glycose residue, i.e. to
a poly- or oligosaccharide residue. These names are
regarded as synonymous with one another. Accordingly, an
alkyl monoglycoside is the acetal of a monosaccharide.
Since mixtures are generally obtained in the acid-catalyzed
reaction of sugars and fatty alcohols, the name alkyl
glycoside is used herein both for alkyl mono-glycosides and
also for alkyl poly(oligo)glycosides and, in particular,
mixtures thereof, including any secondary components,
providing the structural differences are not critical.
Related Art
The surface-active alkyl glycosides have been known
for more than 50 years as ingredients of detergents. Thus,
Austrian patent 135 333 describes the production of lauryl
glucoside and acetyl glucoside from acetobromoglucose and
the particular fatty alcohol in the presence of a base.
Direct synthesis from glucose and lauryl alcohol using
hydrogen chloride as an acidic catalyst is also described
therein. According to the teaching of German patent 611
055, alkyl glucosides are produced from pentaacetyl glucose
and the fatty alcohol in the presence of anhydrous zinc
chloride. The maltosides and lactosides of aliphatic
alcohols containing more than 8 carbon atoms and their use
as surfactants are known from German patent 593 422. For
example, it is stated in this publication that cetyl
maltoside improves the washing effect of soap, which at
that time was the most important surfactant, which is
explained by the effect of cetyl maltoside as a lime soap
dispersant.
1 338237
The 1960's and 1970's saw several proposals for the
improved production of alkyl glycosides either by direct
reaction of the glycose, generally glucose, with an excess
of the alcohol in the presence of an acid catalyst.
Another process comprised reacting a lower alcohol or
glycol as solvent and reactant in the presence of an acid
catalyst to form a primary reaction product, from which the
surface-active alkyl glycoside is obtained by
transacetalization with the relatively long-chain alcohol.
U.S. Patent 3,450,690 (Gibbons et al) describes a
process for the direct synthesis of alkyl glucosides, with
C1-8 alkanols, secondary synthesis products or impurities
which produced unwanted discoloration in the alkaline
medium were removed from the crude product by treatment of
the crude product in aqueous solution while heating with
inorganic or organic bases such as, for example, sodium
hydroxide, sodium methylate, calcium hydroxide, barium
hydroxide, barium methylate or strongly basic amines. The
acidic catalyst (for example sulfuric acid) not only is
said to be neutralized, an alkaline pH value of at least 8
is actually provided. After heating to temperatures of 50
to 200C, the impurities precipitate. They are then
filtered off and the alcohol excess is distilled off. The
aqueous solution in this literature reference is understood
to be the mixture of the excess of the alcoholic reactant
and the water formed during the reaction. In some
Examples, the excess alcohol (ethanol) is removed and
partly replaced by water. After the insoluble precipitate
has been filtered off, the filtrate is lightened by
treatment with active carbon. Bleaching with hydrogen
peroxide is also mentioned as an equivalent measure to the
treatment with active carbon. Calcium hydroxide is
preferably used as the base.
U.S. Patent 3,839,318 (Mansfield et al) describes a
process for the direct glucosidation of long-chain alcohols
1 338~37
in which the reaction rate is controlled through the
reaction temperature and the catalyst concentration in such
a way that the water of reaction formed is quickly removed
from the reaction mixture by azeotropic distillation. A
S hydrocarbon, for example hexane or heptane, is preferably
added as solvent to facilitate the rapid azeotropic
distillation of the water. The reaction mixture is then
neutralized with an aqueous solution of sodium hydroxide
(alkaline pH values may even be provided in this
neutralization step). The excess alcohol is then removed
in the usual way by distillation. Conversion of the
reaction product into an aqueous paste and bleaching of
this paste with sodium perborate are also described.
According to European patent application 132 046
(Procter & Gamble, Letton) the acidic catalyst in a direct
synthesis process is neutralized with an organic base, a
narrow pH range in the vicinity of the neutral point (pH
6.6 to 7 and preferably 6.7 to 6.8) being obtained. The
organic base used is either an alkali (Na, K, Li) or
alkaline earth (Ba, Ca) or aluminum salt of a weak low
molecular weight acid, for example sodium acetate, or a
corresponding alcoholate, for example sodium ethylate.
European patent application 96 917 (Procter & Gamble,
Farris) describes an improved process for acid-catalyzed
direct synthesis, in which a monosaccharide, preferably
glucose, is added continuously or in portions to a mixture
of fatty alcohol and catalyst at 80 to 150C so that never
more than 10% unreacted monosaccharide is present in the
reaction mixture.
According to European patent application 77 167 (Rohm
& Haas, Arnaudis), the color quality of surface-active
al~yl glycosides can be improved by using a typical acidic
catalyst together with an acidic reducing agent from the
group consisting of phosphorous acid, hypophosphorous acid,
sulfurous acid, hyposulfurous acid, nitrous acid and/or
1 338237
hyponitrous acid or the corresponding salts in the produc-
tion of the alkyl glycosides.
According to the teaching of European patent applica-
tion 102 558 (BASF, Lorenz et al), light-colored C3 5 alkyl
glucosides are obtained by production in the presence of an
acidic catalyst and at least equivalent quantities of an
alkali metal salt of a boric acid, preferably sodium
perborate.
It is proposed in European patent application 165 721
(Staley, McDaniel et al) to treat an aqueous solution of a
surface-active alkyl polyglucoside first with an oxidizing
agent, preferably with a hydrogen peroxide solution, and
then with a sulfur dioxide source, for example an aqueous
solution of sodium bisulfite. The products thus obtained
are said to be color-stable, even after prolonged storage.
In the production of surfactant raw materials, efforts
have always been made to obtain substantially colorless
products. Colored impurities or initially colorless
products which discolor in storage are often classified as
low-grade or unuseable unless aesthetically satisfactory
mixtures can be obtained with them. Color stability in
alkaline medium is a particularly important factor in the
further processing of surfactant raw materials.
Although industrial surfactant raw materials can often
be converted into light-colored products, which remain
light-colored even in storage and in alkaline medium, by
bleaching, for example with aqueous hydrogen peroxide
solutions, this bleaching treatment has not been
successfully applied to hitherto known surface-active alkyl
glycosides. Even apparently lightened products reassume a
dark-brown coloration when, after bleaching, they are
treated with aqueous alkali at elevated temperature.
Known processes for the production of alkyl
glycosides, which also seek to improve color quality and
stability in storage, are attended by the disadvantage that
1 338237
either additional chemical agents have to be added during
the production process or the reaction product itself has
to be aftertreated with such chemical agents. The object
of the present invention is to provide a new and improved
process for the production of surface-active alkyl
glycosides by direct synthesis in which a suitable choice
and configuration of the process parameters ensures that
the product bleached in the final step of the process
retains its lightness during storage and further process-
ing, even under alkaline conditions at elevated tempera-
ture. Another object of the invention is to arrange the
process steps in such a way that a minimum of chemical
reactants and a minimum of process measures are required.
A final object of the invention is to select the process
steps in such a way that the process can be carried out on
an industrial scale without any scaling-up problems and is
suitable for the production of surface-active alkyl glyco-
sides in such quantities that the end product can be
processed as a surfactant raw material in the detergent
industry.
Brief Description of the Invention
It has now been found that these and other objects can
be achieved by a novel combination of known and new process
steps into a new direct synthesis process.
Accordingly, the present invention is a process for
the direct production of alkyl glycosides by acetalization
of higher aliphatic primary alcohols with glycoses,
particularly glucose, in the presence of an acidic
catalyst, rapid removal of the water of reaction,
neutralization of the catalyst with a base, removal of the
alcohol excess by distillation and conversion of the
reaction product into an aqueous paste and bleaching of the
paste. The aliphatic alcohol is present in a molar excess
in relation to the glycose and the formation and removal of
the water of reaction is done under reduced pressure and
1 338237
reaction temperatures above 80 C are utilized.
The process comprises
(a) preparing a mixture of aliphatic primary alcohol,
glycose and acidic catalyst in a molar ratio of
qlycose to primary alcohol of from 1:2 to 1:10
and preferably 1:3 to 1:6 at elevated
temperature, by
(1) mixing a portion of the alcohol with the
catalyst, heating the mixture and admixing
a heated suspension of the glycose in the
remaining quantity of alcohol continuously
or in portions to the alcohol/catalyst
mixture;
(2) mixing the entire amount of alcohol and
glycose, heating the mixture and adding the
acidic catalyst to the heated mixture;
(b) reacting the mixture at an elevated temperature
and under reduced pressure, preferably while
mixing, whereby the water of reaction is removed,
(c) cooling the reaction mixture to about 90CC;
(d) adding to the cooled reaction mixture a
sufficient amount of an organic or inorganic
basic alkali metal, alkaline-earth metal,
aluminum or alkali/ aluminum compound to
neutralize the acidic catalyst, and raise the pH
of the mixture to at least 8 and preferably in
the range from 8 to 10 preferably normal pressure
is established after the addition of basic
material;
(e) separating the excess alcohol from the alkaline
mixture under reduced pressure, preferably
without preliminary filtration, to a value below
5% by weight of the reaction product by any of
the methods which do not damage the reaction
1 338237
product; and
(f) cooling the mixture to about 105 to 130C and
adding a sufficient amount of water to produce a
30 to 70% paste and mixing the mixture for about
0.1 to 5 hours at approximately 80C, preferably
an active oxygen compound, preferably hydrogen
peroxide, is added to the mixture with the water
to ensure that the pH of the mixture is
maintained remains at 8 to 10 during the addition
of bleach.
Detailed Description of the Invention
The product of the process is obtained in the form of
a colorless to yellowish aqueous paste. It has
unexpectedly been discovered that the paste retains its
original color quality substantially unchanged during
storage and, particularly during further processing in an
alkaline medium. The color stability of the product is
determined by a simple test. A sample of the product is
mixed with water to form an approximately 50% paste, after
which concentrated sodium hydroxide is added at normal
temperature to bring the pH to about 12 to 13. The paste
is then heated for 30 minutes at 100C. The product of the
process of this invention shows little or no color change
after this treatment. The color values of the products
produced by the process of the invention were determined by
the KLETT method (5% solution in water/isopropyl alcohol
1:1, 1 cm cell, blue filter). Long-term storage tests of
the paste-form product under typical storage conditions and
further processing of the stored product into detergents
and cleaning preparations under alkaline conditions which
this involves, can be reliably simulated by this test
method. The end products of the process preferably have
Klett values of less than 35.
The glycose preferably used in the process of the
invention is glucose. Commercially available glucose often
13,38237
contains 1 mol water of crystallization. The glucose
containing water of crystallization may readily be used,
although the water of crystallization present should be
removed from the reaction medium by thermal measures,
preferably before contact with the acid catalyst. However,
since anhydrous glucose is also commercially available in
large quantities, it is preferred to use anhydrous glucose
in the form of a finely divided powder.
Suitable catalysts comprise acidic compounds,
including the Lewis acids, which catalyze the acetalization
reaction between the fatty alcohol and the sugar molecule.
Of these catalysts, sulfuric acid, phosphoric acid,
aliphatic and/or aromatic sulfonic acids, preferably p-
toluenesulfonic acid, and the sulfoacidic ion exchanger
resins are particularly suitable. Preferred catalysts for
the process according to the invention are sulfuric acid
and p-toluenesulfonic acid which has a less corrosive
effect on appliances and pipes of steel. Acidic ion
exchange resins are also useful in the present process
provided the catalyst is separated from the reaction
mixture after acetalization of the glycose. In such a
case, a suitable basic compound is preferably added after
separation of the acidic ion exchange resin to adjust the
mixture to a pH of 8 to 10.
The conditions under which the three components,
aliphatic alcohol, glycose and catalyst, are mixed may be
varied within wide limits. Thus, in one embodiment of the
process of the invention, it is possible initially to
introduce a mixture of the total quantities of all three
components and to initiate the reaction by heating. In
another embodiment, part of the alcohol is initially
introduced with the catalyst and a heated suspension of the
glycose in the remaining quantity of alcohol is gradually
added. Addition in portions is preferred for laboratory-
scale batches while continuous addition is preferred for
1 3382~
industrial batches. The time intervals at which the
individual portions are added are preferably selected so
that a substantially clear phase is always present, i.e.
the quantity of unreacted glycose in the reaction mixture
is kept very small, i.e. no more than 10%. The mixing
ratio of glycose to aliphatic alcohol may also be varied
within wide limits. It is possible in this way to control
the distribution between alkyl monoglycoside and alkyl
oligoglycosides in the reaction product.
In the case of laboratory-scale batches and,
particularly in the case of industrial-scale batches, it
has been found that a dispersion of fine glycose particles
in the alcohol, particularly the long-chain alcohol, has a
substantial positive effect on the quality of the reaction
product. A fine dispersion is achieved by intensively
mixing a finely powdered glycose, preferably glucose,
optionally after fine grinding, with the alcohol. For
laboratory batches, it has proved to be suitable to use a
high-speed standard laboratory stirrer or even ultrasonica-
tion for this purpose. For industrial batches, inline
mixers, for example a stator/rotor mixer, are preferably
used to produce the fine dispersion. This fine-dispersion
measure has the desired additional effect of heating the
suspension.
A vacuum of approximately 10 to 50 mbar is applied
during formation and removal of the water of reaction. The
mixture is heated and preferably continuously mixed during
the reaction which, in the case of laboratory-scale bat-
ches, is done by simple stirring whereas, in the case of
industrial-scale batches, the mixture is heated and mixed
by pump circulation through an external liquid circuit
incorporating a heat exchanger. During application of the
heat required to maintain the reaction temperature, it is
essential that there be only a slight temperature dif-
ference between the wall of the reactor and the reaction
1 338237
mixture to avoid overheating. To establish this slight
temperature difference, it is sufficient for laboratory-
scale batches to use a standard oil bath with a thermostat
and, at the same time, to vigorously stir the reaction
mixture. In the case of industrial-scale batches, it has
proved to be particularly useful to apply the heat through
an external circuit preferably consisting of a pump and a
heat exchanger. Preferably, part of the reaction mixture
is continuously removed through a pipe, heated in the heat
exchanger and returned to the reactor. In this way, it is
possible to avoid high reactor wall temperatures, i.e.
above 125C, and hence to prevent the color values of the
end product from being adversely affected by temperature.
The aliphatic primary alcohols reacted in accordance
with the invention can basically have any chain lengths,
i.e. from 1 to about 30 carbon atoms. To obtain surface-
active reaction products which are useful as surfactant raw
materials in detergents and cleaning preparations, it is
preferred to use aliphatic primary alcohols containing from
8 to 20 carbon atoms and more preferred from 12 to 18
carbon atoms. These higher aliphatic alcohols are prefer-
ably produced from industrial fatty compounds. However,
synthetic primary alcohols, for example the oxoalcohols,
may of course also be used in the process according to the
2S invention.
Where the portion variant of the process is used, 30
to 70% by weight of the alcohol is preferably initially
mixed with the catalyst, the mixture is heated to 100 to
120C and the glycose is subsequently added, preferably
continuously under a reduced pressure, in the form of a
suspension in the heated remaining quantity of alcohol.
The water of reaction formed is continuously removed from
the reaction mixture. The reaction is regarded as over
when no more water of reaction is eliminated. To determine
the quantity of water of reaction and thus to ascertain the
1 338~37
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end of the reaction, the water may be collected, for
example, by freezing in a cold trap. Accordingly, with
predetermined quantities of mixture and reaction
conditions, the reaction time can be reliably determined
without the water of reaction having to be collected and
measured each time.
In an equally preferred variant where the total
quantity of mixture is introduced, the mixture of alcohol
and glycose is preferably initially introduced and then
heated with stirring, i.e. to a sump temperature of approx-
imately 80C, after which the acidic catalyst is added to
the heated mixture. A vacuum is then applied and the
mixture further heated to approximately 100 to 120C, the
water of reaction formed being distilled off.
Since, as already mentioned, the alcohols may be used
in a wide chain-length range in the process according to
the invention, the vacuum is also adjusted so that the
boiling point of the alcohol is reduced by at least 30C.
For the reaction of the long-chain C1218 fatty alcohols, the
vacuum is preferably adjusted to a value of 10 to 50 mbar.
The higher aliphatic, primary C1218 alcohols particu-
larly useful as the alcohol component are preferably
saturated and, in particular, linear alcohols of the type
obtainable on an industrial scale, by hydrogenation of
native fatty acids. Typical representatives of the higher
aliphatic alcohols which may be used in the process accord-
ing to the invention are, for example, the compounds n-
dodecyl alcohol, n-tetradecyl alcohol, n-hexadecyl alcohol,
n-octadecyl alcohol, n-octyl alcohol, n-decyl alcohol,
undecyl alcohol, tridecyl alcohol. Since the fatty alco-
hols preferably emanate from natural fats, mixtures of
technical fatty alcohols are also usually suitable as
reactants. Besides the actual fatty alcohols, branched-
chain primary alcohols, for example the so-called oxoal-
cohols, are also suitable for the reaction. Typical
1 338237
oxoalcohols are, for example, the compounds C1213 alkanol
with approximately 25% mainly 2-methyl branching (Dobanol
23) and the corresponding Cg11 alkanol (Dobanol 9l). How-
ever, a major advantage of the process is that it can be
used in the production of surfactants obtainable exclusive-
ly from renewable raw materials.
Suitable basic alkali metal, alkaline earth metal, or
aluminum or alkali/aluminum compounds, which may be organic
or inorganic, are, for example, calcium hydroxide, calcium
oxide, magnesium hydroxide, magnesium oxide, the zeolites
NaA or NaX, preferably in combination with calcium
hydroxide, anhydrous sodium carbonate, potassium carbonate,
magnesium and calcium carbonate, sodium methylate, sodium
ethylate, magnesium methylate, magnesium ethylate, sodium
or magnesium propylate or butylate, i.e. the alcoholates of
low-boiling alcohols, preferably C14 alcohols. The
particularly preferred inorganic basic compound is
magnesium oxide while the particularly preferred organic
base is a magnesium alcoholate, more particularly the
ethanolate of magnesium. Both the magnesium oxide and the
magnesium alcoholate may be partly replaced, i.e. up to
half the molecular amount, by powdered sodium hydroxide in
equivalent quantities.
One particular feature of the process is that the
additions of the basic compounds are controlled in such a
way that, over and above neutralization of the acidic
catalyst, an excess of the basic compound is present so
that the reaction mixture shows a distinctly basic reaction
and, hence, preferably has a pH value in the range from 8
to 10. The pH value is measured in a 10% aqueous/alcoholic
mixture of a sample using a standard pH meter.
The alcohol excess is distilled off without damaging
the reaction product by a suitable vacuum distillation
method. The distillation process is carried out under an
absolute pressure of 0.0l to 1 mbar. Basically, the
1 338237
product-protecting distillation also includes the
establishment of a low sump temperature, by which is meant
the temperature of the boiling mixture. In the present
case, however, it has surprisingly been found to be
preferred to heat the reaction mixture to a sump
temperature in the range from 160 to 180C and more
especially in the range from 160 to 170C, and specifically
independently of whether such a high value is actually
necessary at the existing vacuum power for distilling off
the excess alcohol. Such a high sump temperature leads
directly to a crude product with initially poorer color
quality. However, it was unexpectedly discovered that the
products treated at the high sump temperature, after
bleaching, had a lighter color and a better alkali
stability, in the sense of the above-mentioned tests, than
products which had been treated at lower sump temperatures
and had a better color quality prior to bleaching. It is
therefore another important feature of the process of the
invention to bring the reaction mixture, during the process
step of removing the alcohol excess under high vacuum, to
a sump temperature of about 160 to 170C, even if this high
a sump temperature would not be necessary for distilling
off the alcohol excess, such as in the case of the shorter-
chain fatty alcohols.
Generally known vacuum distillation devices can be
used for removing the excess alcohol in the distillation of
laboratory batches. In the case of production-scale
industrial batches, the removal of the excess alcohol is
preferably performed according to a 2-step process. If the
fatty alcohol has a carbon chain length range of 12 to 20,
preferably the reduction of the fatty alcohol fraction to
values of from about 40 to about 20% is performed in a
first step in a thin film evaporator or a falling-film
evaporator. The first step also serves to degass the
reaction mixture. In a second step, preferably using a
1 338237
_.
short-path evaporator, a further fatty alcohol reduction to
the desired final value is carried out. The final content
of fatty alcohol can be less than 0.5 wt% based on the
final product if the product is to be practically free from
the fatty alcohol. When a specific fatty alcohol content
is desired in the final product, these fatty alcohol
contents can be established at about 3 to about 5 wt%. It
has been found that finished products with a fatty alcohol
content of more than 2 wt%, preferably 3 to 5 wt%, based on
the weight of the product have certain advantages in terms
of application.
For gentle separation of temperature-sensitive
mixtures, it may generally be said that falling film
evaporators and, preferably, thin-film evaporators are
particularly suitable for gentle evaporation under reduced
pressure, since extremely short residence times at the
relatively high temperatures necessary can be achieved in
evaporators of this type. In the present case, thin-film
evaporators are particularly useful for removing the excess
C1018 fatty alcohol from the alkyl glycoside with
particularly good surfactant properties.
Thin-film evaporators are evaporators in which a
highly viscous mixture is applied to a heated wall and
mechanically distributed thereon by rotating wiping
elements. Thin liquid layers or liquid films are thus
formed and the film surfaces are continually renewed. The
vapors formed flow countercurrent to the product film and
leave the evaporator through an externally arranged
condenser. Thin-film evaporators are generally operated at
pressures of only a few mbar and the residence time for the
product is only a few seconds. In a two-stage evaporating
method, of the type preferably used in the process of the
invention, the first evaporator also acts as a preliminary
degassing stage for the second stage evaporator. Gases
dissolved in the viscous liquid are removed from the liquid
1 3387~7
during the removal of excess fatty alcohol from the reac-
tion product in the first thin-film evaporator. The short-
path evaporator which is preferably used as the second
stage evaporator is, in principle, a wiped-film evaporator
with a condenser built into the evaporator. These evapor-
ators are suitable for the distillation of high-boiling,
temperature-sensitive products in the range from 101 to
10 4 mbar. In short-path evaporators, as in thin-film
evaporators, the liquid is mechanically distributed over
the heating surface by wipers. According to the invention,
the excess alcohol is removed to almost any residual con-
tents, which may be below 1%, in the short-path evaporator
or thin-film evaporator as the second stage. The two-stage
arrangement of the evaporators provides for high through-
puts in conjunction with the specific establishment of the
desired residual content of fatty alcohol in the end
product. For industrial purposes, thin-film and short-path
evaporators can be dimensioned so that throughputs of up to
300 kg/m2 per hour are readily possible. In principle, the
preferred embodiment of the process according to the
invention with the two-stage fatty alcohol removal step can
also be used in suitable dimensions for working up
laboratory-scale mixtures.
The alkyl glycosides produced in accordance with the
invention are mixtures consisting essentially of alkyl
monoglycoside and the alkyl oligoglycosides, essentially
confined here to di- and triglycosides, and small amounts
of tetra- and pentaglycosides. The distribution between
mono- and oligoglycosides in the end product gives a
theoretical degree of oligomerization of from 1 to 5. The
process is preferably carried out so that the degree of
oligomerization is between about 1 and about 1.5, the
quantity of alkyl monoglycoside, based on the total
quantity, of alkyl monoglycoside and alkyl oligoglycoside
generally exceeds about 70% by weight. (For a definition
1 338237
of the degree of oligomerization, see Paul J. Flory,
Principles of Polymer Chemistry, Cornell University Press,
Ithaca, New York, 1953, pages 35 to 37). The total
quantity of other secondary constituents is generally below
20% by weight. Of these secondary constituents the fatty
alcohol component is variable because it depends upon the
intensity of the fatty alcohol distillation process. The
quantity of residual alcohol in the end products is
adjusted to a preferred range of 0.2 to 5% by weight and
more especially 0.5 to 2.5% by weight. The residues of
unreacted glycose are below 1%. The contents of polymeric
glucose in the end product is from about 2 to about 20% by
weight and preferably from 5 to 20% by weight. The
quantities of the neutralization products of acidic cata-
lyst and basic compound and any excess of this basic com-
pound in the end product are between 0.5 and 1.5% by
weight.
These quantities are based on the reaction product as
its exists immediately after removal of the fatty alcohol
excess by distillation. The actual end product of the
process is an aqueous paste containing 30 to 60% by weight
water which is obtained from the reaction product by treat-
ment with warm water and bleaching with active oxygen com-
pounds, preferably hydrogen peroxide. The quantity of
active oxygen compound is generally from 0.2 to 1.5% by
weight, expressed as H202 and based on the quantity of
product after the removal of alcohol. Since the pH value
falls during the bleaching step, a base, for example sodium
hydroxide, is added together with the per oxygen compound
to maintain pH values in the range from 8 to 10. The
resulting solution or paste preferably contains the salts
emanating from neutralization of the catalyst and the
bleaching process which have not been separated off. It
has been found that there are many applications in which
neither the type nor quantity of these residual salts in
1 338237
_
the aqueous alkyl glycoside paste is problematical. On the
contrary, the compounds in question are in any event
typical constituents of typical detergents and cleaning
preparations.
The pH value of the paste-form end product of the
process is generally left as its accumulates after the
bleaching step, i.e. the paste has a pH value in the range
from 8 to 10. For special applications, the pH may be
reduced to about the neutral point by addition of an acidic
compound which is preferably favorable, but at least not
harmful, to the application envisaged. Suitable acidic
materials are, for example, acidic salts, such as sodium or
potassium hydrogen sulfate, inorganic acids, such as
sulfuric acid, or organic acids, such as citric acid, or
sulfonate or sulfate surfactants in the acid form.
For prolonged storage or prolonged transport of the
paste-form reaction product, it is important to prevent
microbial degradation processes. Accordingly, the paste-
form reaction product prepared in accordance with the
invention preferably contains an antimicrobial effective
quantity of a antimicrobial agent which improves stability
in storage. The antimicrobial additive comprises, for
example, of 0.1 to 0.2% by weight glutardialdehyde.
One particularly preferred embodiment of the process
for the production of light-colored and color-stable alkyl
glycosides by the direct synthesis method is characterized
by application of the following cumulative process steps:
1. The finely divided particulate glycose,
particularly glucose, is dispersed in the
alcohol by high-speed stirrers or by other high-
performance industrial mixers.
2. The base used to neutralize the acid catalyst,
preferably a sulfonic acid, consists completely
or predominantly of magnesium oxide.
3. The quantity of base is calculated so that, over
1 338237
and above the actual neutralization, a basically
reacting mixture, preferably of pH 8 to 10, is
obtained.
4. The reaction mixture is not filtered after the
neutralization step.
5. Finally, during removal of the excess alcohol by
distillation under reduced pressure, the reaction
mixture is heated to a sump temperature of 160 to
180C or the heating temperature in the
evaporator of the second stage is brought to
about 170 to 180C.
The high quality of the end product after bleaching is
attributable to the cumulative application of these process
steps together with the other process steps. This combina-
tion of process parameters may also be applied in the same
way in other processes for the production of alkyl glyco-
sides, for example in the transacetalization process with
butanol or propylene glycol, or in processes where polygly-
coses, particularly starch and starch degradation products,
are used as starting materials.
EXAMPLES
The process according to the invention is illustrated
by the following Examples.
EXAMPLE 1
This Example illustrates a process according to the
invention for the direct synthesis of C12 alkyl glucoside on
a laboratory scale, by the method where a glucose/fatty
alcohol suspension is added in portions (slurry variant).
559 g (3 mol) n-dodecanol and 2.2 g (11.2 mmol) p-
toluenesulfonic acid were introduced into and heated to
between 110 and 114C in a 2-liter three-necked flask
equipped with a stirrer, dropping funnel and water separa-
tion column. A suspension of 180 g (1 mol) anhydrous
19
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glucose (Puridex, a product of Cerestar Deutschland GmbH)
in another 559 g (3 mol) n-dodecanol was then added in
portions, more particularly in 10 portions, at intervals of
5 minutes. A reduced pressure varying from 10 to 15 mbar
was applied before the first addition. The glucose/fatty
alcohol suspension was also heated to about 110~C before
the addition. The water of reaction was removed from the
reaction medium through the distillation head and frozen
and collected in a cold trap cooled with liquid nitrogen.
A total of 19 g water was recovered.
Thereafter, the reaction mixture was stirred for
another 120 minutes at 110 to 115C. The reaction mixture
was then cooled to 90C, after which 2.0 g (17.5 mmol)
magnesium ethylate were added at normal pressure. The
mixture was stirred for 30 minutes. The reaction mixture
had a pH of 9 to 10. The excess alcohol was distilled off
from the reaction flask under a vacuum of 0.1 to 0.01 mbar
and at a sump temperature of 120 to 170C. The quantity of
distillate was 976 g; the distillation residue, i.e. the
actual product, accumulated in a quantity of 299.1 g.
Water and 4.5 g of a 35% H2O2 solution were added to the
residue at a temperature of 90C. The residue was thus
processed with stirring to a 60% by weight alkyl glucoside
paste over a period of 120 minutes. The pH was monitored
during the bleaching process and was maintained at pH 9 by
addition of 50% NaOH.
Product characteristics: hydroxyl value 656; residual fatty
alcohol 0.7%; dodecyl monoglucoside 67% by weight; dodecyl
diglucoside 16% by weight; dodecyl triglucoside 5%; dodecyl
tetraglucoside 2% by weight; dodecyl pentaglucoside 1% by
weight; polyglucose 7% by weight; glucose below 1% by
weight. Klett values: after bleaching: 20; after the color
stability test: 25.
EXAMPLE 2
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This Example illustrates the production of a C1214
alkyl glucoside from anhydrous glucose and a technical
fatty alcohol (mixture of approximately 7S% by weight
dodecanol and approximately 25% by weight tetradecanol) by
the batch embodiment (mixture containing the total quantity
of reaction components) on a pilot-plant scale.
25.0 kg (129 mol) of a dodecanol/tetradecanol mixture
(Lorol S, Henkel KGaA) and 7.7 kg (43 mol) anhydrous glu-
cose (Puridex) were introduced into a 150 liter stainless
steel vessel and heated with stirring to approximately
80C. 53 g (0.28 mol) p-toluenesulfonic acid were than
added to the mixture. The mixture was then heated to
approximately 115C, a vacuum of approximately 20 mbar
being applied at the same time. The reaction mixture was
stirred for about 4 hours under these conditions and the
water of reaction distilled Gff at the reduced pressure.
The resulting yellowish and cloudy reaction solution was
cooled to 90C, after which 35 g (0.87 mol) magnesium oxide
were added under normal pressure, followed by stirring for
30 minutes. A pH of approximately 10 was measured in the
reaction mixture. The alcohol excess was then distilled
off under a vacuum of 0.5 to 1 mbar, the sump temperature
increased to 170C over a period of 3 hours. Approximately
20 kg of fatty alcohol were distilled off during the
distillation process which lasted a total of 3 hours and
was carried out in the reaction vessel. The distillation
residue was an orange-red, clear melt which was cooled to
approximately 105C and then mixed with deionized water at
70C to form an approximately 50% by weight alkyl glucoside
paste. 100 ml 50% sodium hydroxide in one portion and 200
ml 35% hydrogen peroxide in five portions were then added
over a period of 2.5 hours. The reaction mixture was then
stirred for another 5 hours at 80C. 18.9 kg of a light
yellow transparent paste (49.1% water, pH value 9 to 10)
were thus obtained as the reaction product. Product
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characteristics: hydroxyl value 694; residual fatty alcohol
1.8%; monoglucoside 51% by weight; diglucoside 16% by
weight; triglucoside 6% by weight; tetraglucoside 4% by
weight; pentaglucoside 2% by weight; hexaglucoside below 1%
by weight; polyglucose approx. 17% by weight; salts below
2% by weight. Klett values: 20 after bleaching, 20 after
the color stability test.
After storage of the product for 6 months, the color
values and composition (as determined by gas chromato-
graphy) were unchanged.
The color stability of a product produced in accord-
ance with the prior art was determined for comparison.
This product had been produced in accordance with Example
6 of US-PS 3,839,318 (Mansfield~ using a mixture of dodec-
anol and tetradecanol. However, the aqueous sodium hydrox-
ide of Example 6 was not used to neutralize the acidic
catalyst (sulfuric acid), instead sodium methylate was used
as base in accordance with EP 132 046 Bl and the pH value
adjusted to 7Ø The product thus obtained had a Klett
value of 45 and a Klett value of 125 after treatment with
alkali in the color stability test. After conversion into
a 60% paste and bleaching with H202, the Klett values
measured 25 (immediately after bleaching, pH value below 7)
and 110 (after the color stability test). In a repetition
of the experiment, the distillation residue was cooled to
only 130C. The resulting end product had the same
characteristics.
EXAMPLE 3
This Example illustrates the production of C1214 alkyl
glucoside on an industrial scale.
Of the total quantity of 1860 kg C1zl4 fatty alcohol
(distribution: dodecanol approx. 75% by weight, tetradecan-
ol approx. 25% by weight), half was processed with 300 kg
anhydrous glucose (Puridex) in a 2.5 m3 reactor to form a
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suspension. The suspension was finely dispersed by means
of a stator/rotor mixer, undergoing an increase in temper-
ature to 75C in the process. In a second reactor (3.2 m3)
with a distillation column and an external liquid circuit
consistinq of a pump and a heat exchanger, the remaining
fatty alcohol and 3.9 kg p-toluenesulfonic acid were heated
to 115C. The reactor was then evacuated to a pressure of
20 to 30 mbar. The glucose/fatty alcohol suspension was
then continuously added over a period of 1 hour. A total
of 30 kg water was distilled off during this period and an
after-reaction time of 2 hours. The heat required to
remove the water and to maintain the reaction temperature
was introduced into the reaction mixture through the
external liquid circuit. The water of reaction was collec-
ted in a cooled receiver and measured. On completion of
the reaction, the mixture was cooled to 90C. 2.9 kg
magnesium methylate in solid form was then taken in through
the external liquid circuit to neutralize the acidic
catalyst. Normal pressure was then established.
The reaction mixture was then introduced into a thin-
film evaporator of the Sambay type (0.75 m2 evaporator
surface, 8 mbar, approx. 170C) and the excess fatty alco-
hol was removed to a concentration of approximately 32% by
weight of the mixture. The product kept at 135C was low
in viscosity and could readily be transferred to a short-
path evaporator with a roller wiper of the Leybold KD 75
type. The short-path evaporator was operated under the
following conditions: evaporator surface 0.75 m2; operating
pressure 0.075 mbar, as measured in the evaporator; heating
temperature 170C; sump temperature 162C. Alternatively,
a thin-film evaporator was also used in the second
depletion stage in a second batch. In a pressure vessel,
approximately 88 kg water at room temperature were added to
batches of the product (90 kg) in molten form at 150C to
prepare an approximately 50% by weight of alkyl glucoside
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paste. 1.3 kg of a 35% H202 solution and 0.9 kg of a 50%
NaOH solution were added separately. After stirring for 3
hours at 9ooc, the product was cooled to 50C.
Product characteristics: pH 9.5; Klett value 23 (after
bleaching) and 26 after the treatment with alkali and
heating in the color stability test. Composition of the
product (anhydrous): hydroxyl value 650: residual fatty
alcohol 3% by weight; alkyl monoglucoside 62.8% by weight;
alkyl diglucoside 15.4% by weight; alkyl triglucoside 5.8%
by weight; alkyl tetraglucoside 2.5% by weight; alkyl
pentaglucoside 1.1% by weight; alkyl hexaglucoside 0.2% by
weight; polyglucose 6% by weight; glucose less than 1% by
weight; salts less than 2% by weight.
