Note: Descriptions are shown in the official language in which they were submitted.
iZ(~I 36
This invention relates to di-acetals of sorbitol and an
aromatic aldehyde, e.g., dibenzylidene sorbitol. rn one aspect
it relates to an improved method for the manufacture of di-acetals
l~of sorbitol and an aromatic aldehyde.
¦ Di-acetals of sorbitol and aromatic aldehydes, such as,
for instance, dibenzylidene sorbitol, have heretofore been
known as polymer additives for imparting unique properties to
~certain polymers. For examPle, dibenzylidene sorb:itol has
Ibeen employed as a clarifying agent for polyolefins" especiallv
¦polyethylene and polypropylene to improve the transparency of
¦films made from suc:h polyolefins. While the use o:E dibenzvlidene
¦~sorbitol for polymer additives has shown much prom:ise and utility,
¦~problems have nevertheless been encountered in providing
l economical commercial methods for the manufacture of dibenzylidene !
¦ sorbitol having a degree of purity sufficient to justify its
manufacture.
Therefore, an object of the present invention is to
provide an improvecl method for the manufacture of cli-acetals
i such as dibenzvlidene sorbitol by the condensation of sorbitol and
¦ aromatic aldehydes,
Another object of the invention is to provicle an economical
commercially feasible method for producing di-acetals of sorbitol
and an aromatic aldehyde, such as dibenzylidene sorbitol, for use
¦las polymer additives.
1I These and other objects, advantages, and features of the
¦~present invention will be apparent to those skilled in the art
i from a reading of the following detailed disclosure.
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1 115;21~86
According to the present invention, I have disco~ered a
rnethod for producing di-acetals of sorbitol and an aromatic
aldehyde which comprises admixing an effective amount of D-
Isorbitol into an aqueous solution containing a catalytic amount
of a mineral acid so as to form a homogeneous aqueous admixture
containing the mineral acid. Thereafter, an effective amount
of an aromatic aldehyde is incrementally admixed into the
homogeneous aqueoùs admixture containing the D-sorbitol at a
rate sufficient to allow a substantially spontaneolls reaction
between the D-sorb:itol and the aromatic aldehyde, thereby re-
sultiny in an aqueous slurry containing crude di-acetal. The
aqueous slurry of the crude di-acetal is then neutralized and the
crude di-acetal separated from the liquid phase of the neutralized
aqueous slurry. The crude di-acetal is then washed with water to
remove mono-acetal impurities present in the crude di-acetal
product. The washed di-acetal is then dried to rennove sub-
stantially all of the residual water and provide a purified, dry
~di-acetal product.
I ~t should be appreciated with regard to the di-acetals of
¦sorbltol and aromatic aldehyde nnade according to the process of
¦the ~resent invention that what is intended is the disubstituted
compound, e.g., the sorbitol component will be substituted with
two molecules of aromatic aldehyde, ra~her than one or three
molecules. Thus, in the case of benzaldehyde, the condensation
product will be dibenzylidene sorbitol rather than monobenzyli-
dene sorbitol or tribenzylidene sorbitol, which la1:er compounds
may have other utilities but are considered to be, and therefore
115Z~86
¦lare defir)ed as ":i.m~urities" insofar as the r:)re~ent Invention i.s
concer~ed~ Other examr~les of "cli.-aceta~s", as thi-~ t-er[n lS de-
fined according to the present invention include, e.c3., di-
(p-chlorobenzylidene) sorbitol, di(m-chlorobenzvliclene) sorbitol,
di(methylbenzylidene) sorbitol, etc. I
It has been found that a mineral acid should be ~rovided
in the aqueous solution to which the D-sorbitol is added. The
¦acid should be present in a catalytic amount which can vary
~widely and which may depend to a certain extent on the acid
Istrength of the particular acid employed. Generally a catalyti.c
amount is from about 10 to 75 weight percent, preferably from
about 15 to 60 weight percent or even 3~ to 60 weight percent,
based on the total amount of water present in the reaction
mixture. The preferred mineral acids may be hydrochloric acid
and sulphuric acid, although others, such as ortho~.hos~horic acid
mav be employed. When the acid employed is hydrochloric, the
preferred acid conc~ntration has been found to be f:rom about 10
to 25 weight percent, preferably 10 to 20 wei~ht pe.rcent. When
¦sul~hurlc acid is used the preferred concentration may be from
about 30 to 60 weight ~ercent, ~reEerably 35 to 50 weit~ht ~ercent.
The amourlt of D-sorbitol admixed with the aqueous solution ¦
of the mineral acid to form a homogeneous aqueous admixture con-
taininq the mineral acid can vary widely. However, the amoun-t of ¦
D-sorbitol. employed should not exceed the solubility characteris- I
l tics of D-sorbi.tol in tne aqueous solution of the mineral acid at !
the temperature at which the reaction between the D--sorbitol and
laromatic al ehyde is carried out.
115;2~8~
Il Once the desired amount of D-sorbltol has been incorporated
¦¦i.nto the aqueous solution Or the mi.neral acid con-taining the
,amount of mineral acid as heretofore speclfied, an aromatic alde- .
~hyde lS incrementa:Lly added to the homogeneous aqueous admixture
5 ¦containing the D-sorbitol at a rate sufficient to aLlow a sub-
stantially spontaneous reaction to occur between the D-sorbitol
and the aromatic a:Ldehyde. Such incremental addition is generally
achieved b~ very s:lowly adding the aromatic aldehyde to the
aqueous admixture while maintaining the aqueous adm.ixture under
agitation. Further, the amount of aromatic aldehyde added to the
aqueous admixture containing the D-sorbitol is that amount
sufficient to prov:ide a molar ratio of ~-sorbitol to aromatic
aldehvde of from about 1:.75 to about 1:1.75, ~refe:rably about
1:1 to about 1:1.5, or even about 1:1.25 to about 1:1.75.
A wide variety of aromatic aldehydes and mixtures of
aromatic aldehydes may be employed in the process o:E the in-
Iven-tion. Examples oE such aromatic aldehydes include benzalde-
¦hyde, ortho-, para- and meta-tolualdehvde, anisaldehyde and sub-
stituted benzaldehydes having one to three substituents and
wherein the substituents are sclected from lower al}cyl, methoxy,
mono- and di-alkylamino, amino, nitro or halogen. E'referred
aromatic aldehydes include benzaldeh~de, meta- and para-
chlorobenzaldehyde, meta- and para-bromobenzaldehYde and meta-
and para-tolualdehyde.
I The reaction between the D-sorbitol and aromatic aldehyde
to form the desired condensation product can be carried out at
various t mperatures. In the case of benzaldehyde, for instance,
I
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li~Z~
I
~it has been determined that such reaction may be desirably carriedl
jou-t at ambient or room temperatures. In the case of other alde- ;
hydes temperatures above or even below ambient or room temperature~
l may be more suitab:Le.
¦ Once the aromatic aldehyde has been added to the aqueous
admixture containing the D-sorbitol and the minera:L acid and an
aqueous slurry results from the formation of the di-acetal, the
aqueous slurry is neutralized with an alkali substance, such as
sodium hydroxide, potassium hydroxide, sodium bicarbonate and the
like. The amount of alkali material employed may vary widely.
It may be desirable in some applications that the amount of alkali
material employed be slightly in excess of the amount required to
neutralize the aqueous s~urry admixture, although large excesses
of alkali should be avoided.
¦ After the aqueous slurry admixture has been neutraliæed,
¦the crude di-acetal which is the solid material of the aqueous
¦slurry admixture containin~ minor amounts of mono-acetal im-
¦purities, such as monoben~ylidene sorbitol, is separated from the
¦liquid phase of the neutralized at~ueous slurry admixture. It may
be desirable to include the step of washing the crude di-acetal
with cool water to remove any residual salts formed as a result
of the neutralization of the aqueous slurry and excess alkali
material present in the wet, crude di-acetal product. When
washing the wet, crude di-acetal product with cool water, the
temperature of the water can vary widely. However, it is be-
lieved that best r~sults will be obtained when the water is main-
ained at a tem~erature of from about 20~C to about 40C. The
, . I
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1152086
~se~dra~ecl, wet, crllde condensation pro~uc-t ma~ thell bc~ washc~
¦again wi-th warm wa~er to remove the mono-acetal impurities. The
temperature o~ the water employed to wash the crude di-acetal
product to remove mono-acetal impurities can vary widely.
The washed product substantially free of the mono-acetal
impurities may the~eafter be dried to remove residual water and
provide purified, substantially dried di-aeetal product. Drying
ean be aceomplished by any conventional method known in the art,
such as use of a vacuum oven, eonveetion heat and the like. The
drying temperature is not eritieal provided sueh is suffieient to
¦effeetively dry the material but not deeompose sam~e. Subsequent
to drying the puriEied di-aeetal produet may be even further puri-
fled by extraeting same with a relatively non-polar solvent as
will be described hereinbelow in greater detail.
It may be desirable to operate the method for produein~
di-acetal in a continuous or semi-eontinuous method. In sueh
instance, it is desirable that the erude di-aeetal produet be re-
moved from the liquid phase of the aqueous slurry prior to
neutralization so that the reeovered liquid phase can be recycled ¦
or employed ~or further makeup of the initial aqueous solution
of the mineral aeid and the D-sorbitol. In sueh instanee, the
erude solid di-acetal produe-t separated from the liquid phase ean
be neutralized using an aqueous solution of an alkali material,
such as those set forth hereinabove, and thereafter the neutral-
ized produet may be washed using warm water or a eombination of
cool water and warm water as reeited above.
7--
1~ llSZ(~86
The separation of the crude di-acetal product fr~m the
aqueous slurry containing same can be accomplished by any suitable¦
means well known in the art, such as filtration, centrifuging,
and the like.
In order to further illustrate the present invention, the
following examples are given. However, these examples are for
illustrative purposes only and are not to be construed as unduly
limiting the scope of the subject invention as set for~ in the
claims hereafter.
EXAMPLES
. .,
Procedure A
This procedure was employed for Examples 1-3 and 10-12
shown in Tables 1 and 2. A 70 percent aqueous solution of
sorbitol (135 grams, 0.5 mole), the appropriate amount of benzal-
dehyde to give the molar ratio of benzaldehyde to sorbit:ol shown
in Tables 1 and 2, and the designated aqueous mineral ac:id
solution [200 grams) of the concentration indicated, were placed
in a l-liter vessel fitted with a Teflon*~addle stirrer. This
reaction mixture was stirred at about 25C until the viscosity
had risen to the point where stirring was no longer effective.
The acid was then ~eutralized to an extent of about 98 percent
with a 10 percent aqueous solution of sodium hydroxide, and the
reaction mixture finally brought to a pH of about 8 with 10
percent sodium car~onate. The white, solid product was filtered,
washed thoroughly with water, and dried at 95C in a convection
oven.
*Trademark
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~1521~
~j High performance l.iquid chromatography was then used to
determine the ratio of dibenzylidene sorbitol (DBS) to tri-
,benzyl.idene sorbitol (TBS) in the product.
I Procedure B
l~ This procedure was similar to Procedure A except that the
stated molar amount of benzaldehyde was added dropwise to the
reaction mixture over a period of about 4 hours in -the following
¦manner first hour, 50 percent; second hour, 25 percent; third
hour, 15 percent; fourth hour, 10 percent. The reaction was then
continued for a short time to achieve the desired. h:igh viscosity,
neutralized, and the product isolated as described llnder Pro-
cedure A. I
Examples 1-6
l In Example 1 Procedure A was employed using a mole ratio
Iof benzaldehyde to sorbitol that would be -theoretically requi.red
to produce DBS (2:1 mole ratio). The product obtai:ned actually
showed a DBS/TBS ratio of 75:25. By reducing the mole ratio of
benzaldehyde to sorbitol, firstly to 1.5:1, and the:n to 1:1, in
l Examples 2 and 3 respecti.vely, the DBS/TBS ratio in the product
l steadi.ly increased to 83/17. A similar effect was observed in
¦~Examples 4 and 5, where a higher acid concentration was used. The
results are summarized in Table 1.
1~ Examples 6-9
¦1 In Examples 6-9 Procedure B was employed rather than Pro- ¦
cedure A and a lower mole ratio of benzaldehyde to .sorbitol was
also employed resulting in a further increase in the DBS/TBS ratio,
¦¦reaching a maximum ratio of 91:9 in Example 9. The results are
¦Isummarized in Table 1.
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Examples 10-17
"
~, In Examples 10-17 generally similar effec-ts were observed
with a sulfuric acid catalyst. The results are summarized in
,Table 2, where the Aiyher DBS/TBS ratio of 94/6 is observed in
IlExample 17. Examples 10-17 and Table 2 also illustrate that the
percentage yield of product, based on the benzaldehyde employed,
rose very significantly as the mole ratio of benzaldehyde to sor-
bitol is reduced. 'rhis is particularly illustrated by comparing
Examples 12 and 16 with a 40 percent acid concentration.
Although the melting point of a mixture product tended to
¦be broad and somewhat erratic, it was clear from the results in
Tables 1 and 2 that as the DBS/TBS ratio rose significantly, the
melting point of the product also tended to rise as would be ex-
l pected. Again, a comparison of Examples 12 and 16 shows this
¦ effect clearly.
Although the improvement of the DBS/TBS ratio as shown in
Tables 1 and 2 is of great utility, there may still be a need in
certain commercial applications for a product containing an even
~igher proportion o~ the DBS component. According to United States
Patent 4,131,612, a crude DBS product, containing as impurities
TBS and other compounds t may be purified by extracting it with a
~ower aliphatic alcohol, such as methanol, at elevated temperatures .
~his procedure described in the patent using methanol was applied
~¦to the product of Example 17 in Table 2, with the result shown in
I,kable 3. It is seen that the content of DBS in the product
actually declined, rather than increasing as would have been ex-
~ected from the teachings of the abovementioned patent.
-11-
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;l ~152~86
O r-- ~D cr) ~ a N ~D ~1
a~ o cs~ ~1 o o ,--1 N
~, o ~ N .~ N N N N N
l .~ 0~ O~ ~ O O ~ ~ ~
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l ~ m ~ I N ~ N ~I CO (~ 1-- ~
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U~ N ~I N In ~ Ul ~ ~ ~ ~1
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1,l
According to the present invention all or even a portion
of -the TBS present in a di-acetal/tri-acetal pro~3uct may be re-
`~lmoved to increase its di-acetal content by employing a rela-tively
~Inon-polar solvent. In Table 3 are also shown the results of
, extracting DBS/TBS products with relatively non-polar solvents,
viz: toluene and l.,l,l.-trichloroethane. A liquid-to-solid ratio
¦¦of 10:1 was employed as in the case of methanol described above.
¦¦A significant increase in the DBS content was achieved, especially
l in the case of l,l,.l-trichlorethane. The recovery of desired
¦ product was also very high. In the case of the l,l,l-trichlorethan~,
the liquid extract was concentrated to remove the solvent leavin~
a residue with DBS/TBS ratio of 8/92.
TABLE 3
:Extraction DBS:TBS Ratio
l Solvent ConditionsInitial FinalRecovery
Methanol 1 Extraction 94:6 93:7 ~ 90%
r~'60~c
Toluene 3 Extractions 92:8 95:5 v 85%
" ~J80C
l,l,l-Trichloro- 3 Extractions 92:8 98:2 ,~90
ethane ,~/70C
Example 18
I A 70~O aqueous D-sorbitol solution (52 grams, 0.2 mole
¦~orbitol) and 48~ sulfuric acid (87.1 grams) were placed in a flask¦
¦~ith stirrer. Benzaldehyde (31.5 grams, 0.3 mole) was then added
¦~ropwise with vigorous stirring over a period of 1 hour and 45
¦~inutes. During the addition, the temperature of the reaction
Il
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1 115;;:(~86
, .
mixture rose from 24 to 28C, and a pale yellow solid was formed.
Continued stirring of the slurry for a further 1 hour and 30
llminutes. Poured the contents of the flask into 8% aqueous sodium
jlhydroxide with vigorous stirring to neutralize the acid. Then
l¦filtered off the solid, and washed i-t with cold water to a pH of
5.5. Slurried the solid product in water at 90C for 30 minutes, I
then filtered, and washed the material with more hot water. Dried ¦
the product in a vacuum oven to constant weight. Y:ield: 42 grams
l (78% yield calculated as dibenzylidene sorbitol, and based on the
weight of benzaldehyde employed.) The melting point of the off-
white powder was 197-202C, versus the literature melting point
for dibenzylidene sorbitol of 224C. Elemental analysis gave:
C, 68.7; H, 6.05~. (Calculated for C20H22O6: C, 67.0; H, 6.2%.)
Example 19
ll The procedure used was essentially similar to that of
llExample 18, except that the amount of benzaldehyde was increased
¦'(41 grams, 0.39 .nole). In this case, the yield of product was
50.8 grams (74% based on the benzaldehyde), but the melting point
was lower, viz: 175-179C. ~Found: C, 69.1; H, 6.0)
¦ Example 20
Following a similar procedure to Example 18, but with a
reduced amount of benzaldehvde (21.2 grams, 0.2 mole) the yield
~of solid product was 25.2 grams (70% based on the benzaldehyde).
I¦The melting point of this material was again lower: 173-177C.
Found: C, 67.5; H, 5.3) .
--1 4--
2~
!! Example 21
, i :
Again repeated the procedure of Exam~le 18, but lowered
the concentration of the sulfuric acid from 48~; to 32% by weight.
IlAfter completion of the benzaldehyde addition and subsequent
¦Istirring period, there was relatively little solid present. Heate~
the reaction mixture to 70C for 1 hour, then cooled overnight,
whereupon the reaction mass solidified. On working up the
reaction as described there was obtained: 36.1 grarns of product
(52% yield on the benzaldehyde); melting point 170-:L75C. (Found:~
C, 68.9; H, 6.2).
The above melting point data provided in Examoles 18
through 21 is believed to show the improved purity of dibenzyliden~
sorbitol employing the concept of the present lnvent:ion wherein
l the amount of sorbitol to benzaldehyde is maintainecl in the
¦¦specified mole ratio and the benzaldehyde is contact:ed with the
D-sorbitol in such a manner as to allow such reactants to react
substantially simultaneously, thus preventing the formation of
,undesired side products.
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