Note: Descriptions are shown in the official language in which they were submitted.
1 ~.32306
Phenolic Antioxidant
THIS I~VENTIO~ relste6 to tris(l-hydroxy-3-methyl-6-tert.
butyl phenyl) butane, a phenolic antioxidant. More part~cularly, it
concerns a process for producing that compound in a purifled form.
We first described a group of novel phenolic derlvatlves
having important antioxidant properties, and a process for their
preparation, in United Kingdom Patent No. 951,935. Among the
compounds which we described was tris(l-hydroxy-3-methyl-6-tert. butyl
phenyl) butane. It was produced by condensing crotonaldehyde with
3-methyl-6-tert. butyl phenol. The product has for many years been
sold under the Trade Mark "Topanol" CA.
The product may be produced by carrying out the condensation
in a solvent, ior example methanol, and in the presence of a
condensing agent, for example hydrochloric acld. The crude product
may be isolated as a solid and may then be washed with water,
whereafter it may be recrystallised from toluene, for example. ~See
for example, page 2 line~ 55-64 of the above specification3. In
another embodiment, the product may be obtained by adding an
entraining agent, preferably toluene, to the reaction mlxture,
d'istilling the mixture to remove water of condensation and finally
recovering the product by crystallisation from the remaining
entrainlng agent. (See page 2, lines 23-3~ of the above
specification).
-When the production of tris(l-hydroxy-3-methyl-6-tert. butyl
phenyl~ butane include~ a final recrystallisation from a C6 to-Cg
aromstic hydrocarbon for example toluene, the product may contain
a quantity of the hydrocarbon in the crystals. For many antioxldant
uses the presence of the said hydrocarbon may be acceptable but in
some uses it may be desired to use a product from which the
hydrocarbon has been at least partly removed. One way of producing
the product ~ith a minimum aromatic hydrocarbon content is to subject
the product to controlled heating, to remove some at least of the
hydrocarbon present. Another way i8 to carry out a recrys~allisation
from another solvent. Yet another way is to omit the crystallisation
from the aromatlc hydrocarbon but this is a desirable feature of the
well-establlshed production method.
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We have therefore devised an alternative process for
producing tris(hydroxy-3-methyl-6-tert. butyl phenyl) butane of low
aromatic hydrocarbon content, which represents a readily achieved
modification of the well-proven existing process.
According to the present invention a process of purlfying
tris(1-hydroxy-3-methyl-6-tert. butyl phenyl) butane compri~es
crystallising it from an aromatic hydrocarbon having 6 to 9 carbon
atoms to produce a product containing said hydrocarbon and
removlng at least part of the hydrocarbon from the product by washing
it w5th a liquid consisting essentially of at least one water-miscible
alcohol and water.
The tris(l-hydroxy-3-methyl-6-tert. butyl phenyl) butane may
be made by condensing crotonaldehyde with 3-methyl-6-tert. butyl
phenol as described in UK Patent 951,935. Aldol may be used as an
alternative to crotonaldehyde if desired. In forming the desired
product three mo]ecules of 3-methyl-6-tert. butyl phenol condense
with each-molecule of crotonaldehyde or aldol.
The alcohol (or alcohols lf more than one is employed) may
be a monohydric, dihydrlc or trihydric alcohol and may have a
s~raight- or branched-chain or cycloaliphatic structure. Preferably
it contains a maximum of six carbon atoms, and while ethylene glycol
and glycerol are believed to be suitable alcohols in appropriate
circumstances, it is preferred that the alcohol be a Cl to C6
straight- or branched-chain or cycloaliphatic monohydric alcohol.
Preferred alcohols therefore include methanol, ethanol, n- and
isopropanol, n-, ~ec. and tert. butanol, n-amyl alcohol and
cyclohexanol. A~ong these, methanol, ethanol, isopropanol and tert.
butanol are preferred and methanol is particularly preferred. If
desired, mixtures of alcohols may be employed, ior example in order
to achieve a balance between the desirable relevant properties of
the individual alcohols.
The water content of the liquid depends upon the alcohol
or alcohols selected but normally (when miscibility permits) will
lie in the range of 10 per cent to 90 percent by weight. When u6ing a
Cl to C6 monohydric alcohol, the process may be operated to
particular advantage by employing a mixture containing between
3 H.32306
50 and 90 per cent by weight of water. FurLhermore, within this
range, a good balance between product yield on the vne hand and low
aromatic hydrocarbon content of the product on the other, may be
obtained by using an alcohol/water mi~ture containing between 65 and
85 percent by weight of water. Ideally, the liquid is so formulated
as to maximise the hydrocarbon removal while minimising the ~olubility
of the tris-phenolic compound in the liquid. The solubility of the
compound in the alcohol itself increases, in the case of homologous
monohydric alcohols, as the carbon number of the alcohol increases;
however, the solubility of the compound in water is very low.
Therefore, in order to limit the solubility of the compound in the
washing liquid, the water content of the liquid should preferably be
increased with increasing alcohol carbon number.
The washing of the crystals of tris (hydroxy-3-methyl-6-tert.
butyl phenyl) butane may conveniently be carried out at ambient
temperature. Sincel however, the solubility of the phenolic compound
in the alcohol and in water varies with temperature, it is possible
to carry out the washing at an elevated temperature, ~ay 60C9 ~o
enable the use of a different alcohol or a different water content,
f~om that which is appropriate at ambient temperature - for example to
make possible the use of less alcohol in the aqueous alcohol wash
mixture.
The quantity of aqueous alcohol employed conveniently is
such that its weight is 1 to 5 tlmes the weight of the phenollc
compound. The optimum quaneity may be determined by experiment and
depends upon such factors as the composition of the aqueous alcohol,
the desired purity of the washed product and the wash procedure
selected. Often the optimum quantity will be 2 to 3 tlmes the weight
of the phenolic compound.
After the washing, the wet crystals may be subjected to
drying, for example at an elevated temperature of 60C to 80~, to
remove residual wash liquor.
The invention ~s illustrated by the following Examples, in
which percentages are by weight.
EXAMPLES 1 TO 3
246 g of 3-methyl-6-tert. butyl phenol ~1.5 moles), 175 g
of methanol and 87.5 g of concentrated hydrochloric acid were heated
4 H.32306
together, with stirring, until the methanol refluxed gently and then
35 g of crotonaldehyde (0.5 mole) was added 810wly while the mixture
was stirred. The resulting mixture was then held under reflux for
a further one hour. A solution of anhydrous sodium carbonate (13 g
in 150 ml water) was then added to neutralise the catalys~ acid.
Methanol was distilled from the stirred reaction mi~ture
until the temperature reached 98C and then 750 g of toluene was
slowly added to dissolve the crude tris(hydroxy-3-methyl-6-tert. butyl
phenyl)butane. The mixture separated into two layers and the lower
(aqueous) layer containing dissolved neutralisation products was
drained off, the upper (organic) layer being maintained at about
85C.
The organic layer was now washed twice with 250 ml of water
and finally the organic layer was allowed to cool to room temperature
with stirring. The tris-phenolic product which crystallised out was
filtered off and allowed to dry. The product was analysed and found
to contain 1.2 per cent of water, 2.6 per cent of methanol and 11.1
per cent of toluene.
A 50-gm portion of thi6 primary product was subjected to
washing with 200 ml of a methanol/water mixture, the phenolic compound
and the mixture being mixed together over a period of 30 minutes
before removal of the washed product by filtration. The product was
now dried in a fan-assisted oven for 4 hours at a temperature of 69C.
Finally, the dried product was weighed and analysed for water,
methanol and toluene, with the following results:-
Uater in Product Product Analysls (% wt)
Example Wash Liquld ~eight
No.(% wt) (gm.) Water Methanol Toluene
1 24 42.9 1.0 3.7 0.3
2 56 44.0 0.3~ 0.5 2.7
3 75 43.7 0.24 0.6 2.0
EXAMPLE 4
A 50-~m portion of tris~hydro~y-3-methyl-6-tert. butyl
phenyl) butane, prepared as described in the above E~amples ~the
primary product~ foLlowing crystallisation from the organic layer),'
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was washed for half-an-hour with 200 ml of aqueous isopropanol
contain~ng 75 per cent of water and then separated by filtration.
Drying the solid for four hours at 70C yielded 47.4 gm of product
which on analysis was found to contaln 0.27 per cent of ~ater,
9.3 per cent of isopropanol and only 0.4 per cent of toluene.
EXAMPLE _
The preceding Example was repeated using 50 gm of phenolic
compound and 200 ml of aqueous tert. butanol containing 75 per cent
of water. 50.0 gm of product was obtained, containing 0.23 per cent
of water, 14.6 per cent of tèrt. butanol and only 0.7 per cent of
toluene.
EXAMPLE 6
240 g of 3-methyl-6-tert. butyl phenol (1.5 moles), 175 g
of methanol and 87.5 g of concentrated hydrochloric acid were heated
together, with stirring, until the methanol refluxed gently and then
35 g of crotonaldehyde (0.5 mole) was added slowly while the mixture
was stirred. The resulting mixture was then held under reflux for
a further one hour. A solution of anhydrous sodium carbonate (13 g
in 150 ml water) was then added to neutralise the catalyst acid.
~ Methanol was distilled from the stirred reaction mixture
until ehe temperature reached 98C and then 750 g of toluene was
slowly added to dissolve the crude tris(hydroxy-3-methyl-6-tert. butyl
phenyl) butane. The mixture separated into two layers and the lower
(aqueous) layer containing dlssolved neutralisation products was
drained off, the upper (organic) layer being maintained at about
85C. - `
The organic layer was now washed twice with 250 ml of water
and finally the organic layer was allowed to cool eo room temperature
with stirring. The tris-phenollc product which crystallised out was
removed. The product at this stage was found to contain 10.8 per
cent of toluene and 1.5 per cent of water.
The crystals were now washed with 450 ml of aqueous methanol,
containing 25 per cent by weight of water. After this wash treatment
and subsequent drying for 4 hours in a fan-assisted oven at 68C,
the crystals were now found to contain 2.5 per cent of water, 3.4
per cent of methanol and only 0.8 per ceDt of toluene.
