Process for producing a linear trimer of paraisopropenyl phenol

A novel trimer of p-isopropenyl phenol of the structure ##STR1## which is useful as a material or a curing agent for epoxy resins. The linear trimer includes a cis-isomer (m.p. 225.5.degree.-227.degree. C.) and a trans-isomer (m.p. 167.degree.-168.degree. C.). It is prepared by reacting p-isopropenyl phenol or its linear polymer in the presence of an acid catalyst such as sulfuric acid, boron fluoride or activated clay in an aromatic hydrocarbon, halogenated hydrocarbon, substituted aromatic hydrocarbon or aprotic polar solvent (e.g., benzene, carbon tetrachloride, nitrobenzene or dioxane).

This invention relates to a process for producing linear trimer of 
p-isopropenyl phenol, and. 
The present invention provides a process for producing a novel linear 
trimer of p-isopropenyl phenol represented by the formula 
##STR2## 
which is termed 2,6-dimethyl-2,4,6-tris(4-hydroxyphenyl)-hept-3-ene. This 
linear trimer includes cis- and transgeometric isomers. 
FIGS. 1 and 2 are infrared absorption spectra of the linear trimers 
obtained in Examples 1 and 10, respectively. 
One known linear trimer of p-isopropenyl phenol is 
4,6-dimethyl-2,4,6-tris(4-hydroxyphenyl)-hept-2-ene of the formula 
##STR3## 
The compound of formula [II] is produced by adding 37% hydrochloric acid 
to a 50% acetic acid solution of monomeric p-isopropenyl phenol to adjust 
the pH of the solution to 1, and reacting the solution at 25.degree. C. 
for 18 to 24 hours, as disclosed in U.S. Pat. No. 3,288,864. According to 
this method, the final desired product is difficult to isolate, and a long 
period of time is required for its production. Hence, it cannot permit 
low-cost commercial production. 
U.S. Pat. No. 4,054,611 states that p-isopropenyl phenol is a readily 
polymerizable compound which polymerizes to a polymer expressed by the 
formula 
##STR4## 
wherein n is 0 or an integer of 1 or more. A polymer of formula [III] in 
which n is 1 corresponds to the linear trimer of p-isopropenylphenol of 
formula [II]. A polymer of formula [IV] in which n is 1 has a somewhat 
different structure from the linear trimer of p-isopropenylphenol 
expressed by formula [II]. 
Although some linear trimers of p-isopropenyl phenol have been known as 
described above, a compound of formula [I] has not yet been known. 
According to this invention, the linear trimer of p-isopropenyl phenol 
expressed by formula [I] can be advantageously produced by reacting at 
least one compound selected from the group consisting of p-isopropenyl 
phenol and linear polymers of p-isopropenyl phenol in the presence of an 
acid catalyst in an organic solvent. 
The method for producing p-isopropenyl phenol, one of the starting 
materials in this invention, is well known. It can be obtained, for 
example, by heating bisphenol A to a high temperature in the presence of a 
basic catalyst to cleave it into phenol and p-isopropenyl phenol, 
distilling out these products under reduced pressure out of the reaction 
system, rapidly cooling the distillates to a temperature below the melting 
point of these distillates to solidify them, and recrystallizing the 
resulting solid from a solvent. p-Isopropenylphenol can be used as a 
starting material in this invention either singly or together with linear 
polymers of p-isopropenyl phenol. 
The linear polymer of p-isopropenyl phenol, as another starting material in 
this invention, is a linear polymer of p-isopropenyl phenol of formula 
[III] or [IV] above, or mixture thereof having a degree of polymerization 
of 2 to 10 (n is 0 to 8 in formula [III] or [IV]). This linear polymer is 
obtained, for example, by heating bisphenol A in the presence of a basic 
catalyst to cleave it into phenol and p-isopropenyl phenol, distilling out 
these products out of the reaction system under reduced pressure, cooling 
the distillates to liquefy them, and then removing the phenol from the 
liquefied product by vacuum distillation. Since p-isopropenyl phenol is 
readily polymerizable, especially in the liquid state, and therefore, 
while p-isopropenyl phenol is maintained liquid (namely, from the 
liquefaction to the end of vacuum distillation), a part or a greater part 
of it polymerizes to a linear polymer. Sometimes, this linear polymer 
contains monomeric p-isopropenyl phenol, but can be used as a starting 
material in this invention without any degradative effect. 
p-Isopropenyl phenol can also be obtained by dehydrogenating p-isopropyl 
phenol at 500.degree. to 600.degree. C. by using a chromia-alumina 
catalyst, or by decomposing 
p-2-hydroxy-2-propyl-.alpha.,.alpha.'-dimethylbenzylhydroperoxide obtained 
by oxidation of p-diisopropyl benzene, in the presence of an acid 
catalyst. Heating of such p-isopropenyl phenol in the liquid state can 
afford its linear polymers of formula [III] or [IV]. p-Isopropenylphenol 
and linear polymers thereof thus obtained can also be used as starting 
materials in this invention. 
The linear polymers may have a structure of formula [III] or [IV], or a 
mixture thereof. When the linear polymer is used as a starting material in 
this invention, the linear trimer of p-isopropenyl phenol of formula [I] 
can be formed not only from a dimer but also from a trimer or higher 
polymer when the above linear polymers are used as starting materials in 
this invention. 
Japanese Patent Publication No. 10869/77 discloses that a linear polymer of 
p-isopropenyl phenol containing a major proportion of a mixture of 
4-methyl-2,4-bis(4-hydroxyphenyl)-pent-1-ene and 
4-methyl-2,4-bis(4-hydroxyphenyl)-pent-2-ene, two isomeric dimers of 
p-isopropenyl phenol, is obtained by a process which comprises heating 
bisphenol A in the presence of a basic catalyst to cleave it, distilling 
off phenol from the resulting cleavage product containing the phenol, 
monomeric p-isopropenyl phenol and a linear polymer of p-isopropenyl 
phenol to form a mixture containing less than 10% by weight of phenol, and 
heating the mixture to 80.degree. to 150.degree. C. Usually, the above 
linear dimers of p-isopropenyl phenol include at least 85% by weight of 
4-methyl-2,4-bis(4-hydroxyphenyl)-pent-1-ene and not more than 15% by 
weight of 4-methyl-2,4-bis(4-hydroxyphenyl)-pent-2-ene. The analysis made 
by the present inventors led to the confirmation that the linear polymer 
of p-isopropenyl phenol obtained by the above method contains at least 80% 
by weight of the above dimeric mixture, 7 to 13% by weight of a linear 
trimer of formula [III] or [IV], 5 to 9% by weight of a linear tetramer, 
and 2 to 4% by weight of a pentamer or higher polymer. This linear polymer 
of p-isopropenyl phenol containing the linear dimers as a major component 
can be used as a starting material in this invention either as such or 
after recrystallization to remove the other ingredients. 
Since p-isopropenyl phenol is unstable and readily polymerizable, it is 
difficult to handle as a starting material. On the other hand, the rate of 
formation of the linear trimer of p-isopropenyl phenol of formula [I] from 
a linear polymer of p-isopropenyl phenol having a degree of polymerization 
of 4 or more is relatively slow. In contrast, the above linear dimers of 
p-isopropenyl phenol and linear polymer of p-isopropenyl phenol containing 
these dimers as a major ingredient are easy to handle and readily soluble 
in organic solvents, and the rate of formation of the linear trimer of 
p-isopropenyl phenol of formula [I] from these materials is sufficiently 
fast. Accordingly, they are especially suitable as starting materials for 
the linear trimer of p-isopropenyl phenol of formula [I]. 
In the production of the linear trimer of p-isopropenyl phenol of formula 
[I] in this invention, an organic solvent is used. Examples of useful 
organic solvents are aromatic hydrocarbons such as benzene, toluene or 
xylene; halogenated hydrocarbons such as methylene chloride, carbon 
tetrachloride, chloroform or ethylene dichloroide; substituted aromatic 
hydrocarbons such as nitrobenzene, anisole or chlorobenzene; and aprotic 
polar solvents such as dioxane, dimethyl formamide, dimethyl acetamide, 
acetonitrile, nitromethane or tetrahydrofuran. These organic solvents can 
be used either singly or as a mixture of two or more. A mixture of an 
aromatic hydrocarbon with water or an alcohol such as methanol or ethanol 
can also be used. In this case, the amount of water is preferably not more 
than 3.0% by weight based on the total weight of the mixture, and the 
amount of the alcohol is preferably not more than 70% by weight based on 
the total weight of the mixture. The amount of the organic solvent is not 
particularly critical. Usually, it is 20 to 1,000 parts by weight, 
preferably 50 to 200 parts by weight, per 100 parts by weight of the 
starting material. 
Examples of the acid catalyst used in the production of the linear trimer 
of p-isopropenyl phenol of formula [I] include Lewis acids such as 
aluminum chloride, ferric chloride, stannic chloride or boron trifluoride, 
protonic acids such as sulfuric acid, phosphoric acid, hydrochloric acid, 
perchloric acid, benzenesulfonic acid, toluenesulfonic acid or 
methanesulfonic acid; and solid acids such as silica alumina, activated 
clay or cation exchange resins. The acid catalyst is used generally in an 
amount of 0.001 to 10 parts by weight per 100 parts by weight of the 
starting material. The especially preferred amount is 0.01 to 0.5 part for 
the protonic acid, cation exchange resin or Lewis acid, and 1 to 2 parts 
by weight for the activated clay, both per 100 parts by weight of the 
starting material. 
The reaction temperature is generally from 0.degree. C. to 100.degree. C., 
preferably 35.degree. to 65.degree. C. At higher than 100.degree. C., 
side-reactions such as the formation of a cyclic dimer of p-isopropenyl 
phenol tend to take place, and the yield of the desired product decreases. 
At lower than 0.degree. C., oligomers of p-isopropenylphenol having a 
higher molecular weight than the trimer tend to form. 
The reaction time is not particularly limited, but the suitable time is 0.1 
to 10 hours. 
The ratio between the cis- and trans-isomers of the linear trimer of 
p-isopropenyl phenol of formula [I] has closely to do with the reaction 
temperature and time. When the reaction is performed under the aforesaid 
conditions, the trans-isomer generally forms earlier, and the formation of 
the cis-isomer is delayed. For this reason, when the reaction time is 
relatively short, the product contains a higher proportion of the 
trans-isomer and a lower proportion of the cis-isomer. However, on 
continuing the reaction, isomerization of the trans-isomer to the 
cis-isomer takes place. Thus, when the reaction is performed for a 
relatively long time, the product contains a higher proportion of the 
cis-isomer and a lower proportion of the trans-isomer. 
This tendency is more outstanding as the reaction temperature is higher. 
For example, when the reaction temperature is at least 65.degree. C., the 
linear trimer formed by reaction within 1 hour consists of 80 to 90% of a 
trans-isomer and the remainder being a cis-isomer. When the reaction is 
performed for 4 hours or more, the product contains 80 to 90% of the 
cis-isomer, and the remainder being the trans-isomer. At a lower reaction 
temperature, the above tendency is less outstanding, and even when the 
reaction time is relatively short, the proportion of the cis-isomer in the 
product is higher. For example, when the reaction is performed at 
60.degree. C. for about 2 hours, the cis-isomer becomes a major ingredient 
of the product, and the proportion of the trans-isomer decreases. 
Accordingly, products having the cis-isomer and the trans-isomer in 
various desired ratios can be obtained by properly choosing the reaction 
temperature and time. 
Specifically, the linear trimer of p-isopropenyl phenol of formula [I] is 
produced, for example, by feeding p-isopropenyl phenol and/or a linear 
polymer of p-isopropenyl phenol as a starting material and an organic 
solvent into a reactor, maintaining them at a predetermined temperature 
with stirring, adding a suitable amount of an acid catalyst, and 
maintaining the mixture for a certain predetermined period of time. The 
reaction can be performed in an atmosphere of air, and an inert gaseous 
atmosphere such as nitrogen or helium is not essential. Preferably, the 
starting material is kept uniformly dissolved in the organic solvent at 
the time of adding the acid catalyst and initiating the reaction. However, 
even when the material is not uniformly dissolved at this time, it will be 
so dissolved as the reaction proceeds after the addition of the acid 
catalyst. 
When a non-polar organic solvent such as an a aromatic hydrocarbon or 
halogenated hydrocarbon is used as the solvent in the above reaction, the 
product precipitates as crystals as the reaction proceeds. On the other 
hand, no precipitation of the product takes place when a polar organic 
solvent such as dimethyl formamide, dioxane, nitrobenzene or acetonitrile 
is used. 
The composition of the reaction mixture is intermittently analyzed by gas 
chromatography, and when no change is noted in the concentrations of the 
starting materials, the reaction is regarded as terminated. 
After the reaction, an aqueous solution of an alkali such as sodium 
hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate is 
added to neutralize the acid catalyst. 
After the neutralization of the acid catalyst, the reaction product is 
separated from the reaction mixture by various methods depending upon the 
state of the reaction mixture. Specifically, when the organic solvent is 
non-polar and therefore, the product separates as a precipitate, the final 
product is obtained by filtration. When the organic solvent is polar and 
therefore, the product is not precipitated, a non-polar solvent such as 
benzene is added to the reaction mixture to dilute it and thereby to 
precipitate the product as crystals. The final product is obtained by 
separating the crystals through filtration. Prior to adding the non-polar 
solvent, the reaction mixture may be distilled under reduced pressure to 
distill off a part of the polar solvent from the reaction mixture. 
According to this invention, the linear trimer of p-isopropenyl phenol of 
formula [I] can be easily prepared selectively from p-isopropenyl phenol 
and/or its linear polymer by performing the reaction for a relatively 
short period of time. The desired linear trimer can be easily separated as 
a precipitate from the reaction mixture. 
The linear trimer of p-isopropenyl phenol represented by formula [I] 
obtained as above can be converted, without purification, into useful 
derivatives by such reactions as epoxidation or hydrogenation. 
Recrystallization from a suitable organic solvent, for example a lower 
alcohol such as methanol or ethanol can, of course, afford a linear trimer 
of higher purity. The high purity linear trimer so obtained can be used as 
a raw material for thermosetting resins or as a curing agent for epoxy 
resins either as such or after conversion into its derivatives. 
For example, when the unpurified product is hydrogenated in a stream of 
hydrogen at 200.degree. to 300.degree. C. under atmospheric pressure using 
10% Pd on diatomaceous earth as a catalyst, a compound of the following 
formula is obtained. 
##STR5## 
This compound can be used as a curing agent for epoxy resins, and its 
epoxidation product is useful as a raw material for epoxy resins. 
When the linear trimer of p-isopropenyl phenol represented by formula [I] 
obtained as above is treated, without purification, with epichlorohydrin 
in the presence of sodium hydroxide, it can be converted to an epoxy 
compound of the following formula [VI]. 
##STR6## 
This compound is extremely useful as a raw material for epoxy resins. 
In one example of application of the linear trimer of this invention as a 
curing agent for an epoxy resin, 1 mole of the linear trimer of 
p-isopropenyl phenol of formula [I] which is purified by recrystallization 
is mixed with 1.5 moles of a diglycidyl ether of bisphenol A, and after 
adding a catalytic amount of N,N-dimethylbenzylamine, the mixture is 
heated at 160.degree. C. for 1 hour to afford a pale yellow clear cured 
epoxy resin.

The following Examples illustrate the invention more specifically. All 
parts and percentages in these Examples are by weight. 
EXAMPLE 1 
A glass reactor was charged with 50 parts of benzene and 100 parts of a 
mixture of linear polymers of p-isopropenyl phenol which had been prepared 
by the method disclosed in Japanese Patent Publication No. 10869/77 
(consisting of 83% of a dimer, 4.3% of a trimer, 2.1% of a tetramer, 0.9% 
of a pentamer and 1.5% of a hexamer and higher polymers), and they were 
maintained at 50.degree. C. Separately, a 10% aqueous solution of 
hydrochloric acid was prepared, and 0.5 part of the solution was fed into 
the reactor. With stirring, the reaction was performed at 50.degree. C. 
for 4 hours. The reaction mixture was then neutralized with a 10% aqueous 
solution of sodium hydroxide, and the precipitated crystals were separated 
by filtration. The crystals were dried, and weighed. The weight was found 
to be 74.5 parts. Recrystallization from methanol afforded 68 parts of a 
linear trimer of p-isopropenyl phenol of formula [I] having a purity of 
98% as determined by gas chromatography and a melting point of 
225.5.degree. to 227.degree. C. The resulting linear trimer consisted of 
more than 95% of the cis-isomer and the remainder being the trans-isomer. 
The chemical shifts (.delta. values) of the nuclear magnetic resonance 
spectrum of the linear trimer in acetone-D.sub.6 were as follows; 
##STR7## 
______________________________________ 
a CH.sub.3 0.87 ppm 
b CH.sub.3 1.38 
c CH.sub.2 2.50 
d CH 5.63 
e -.phi. -OH 7.83 
f -.phi. -OH 8.00 
______________________________________ 
The infrared absorption spectrum (KBr method) of the linear trimer is shown 
in FIG. 1. 
EXAMPLE 2 
Example 1 was repeated except that the amount of the benzene was increased 
to 100 parts, and the amount of the 10% aqueous solution of hydrochloric 
acid, to 2 parts. There was obtained 83 parts of the same linear trimer of 
p-isopropenyl phenol as obtained in Example 1. 
EXAMPLE 3 
Example 1 was repeated except that the reaction was performed at 80.degree. 
C. There was obtained 40 parts of the same linear trimer of 
p-isopropenylphenol as obtained in Example 1. Large amounts of a cyclic 
dimer of p-isopropenyl phenol and bisphenol A were formed as by-products. 
EXAMPLE 4 
Example 1 was repeated except that 10 parts of methanol was added further 
as a solvent. After a 4-hour reaction, 50 parts of the same linear trimer 
of p-isopropenyl phenol as obtained in Example 1 was obtained. 
EXAMPLE 5 
Example 1 was repeated except that 500 parts of methylene chloride was used 
as the solvent and the reaction was performed at 25.degree. C. There was 
obtained 71 parts of the same linear trimer of p-isopropenyl phenol as 
obtained in Example 1. 
EXAMPLE 6 
Example 1 was repeated except that 100 parts of a linear dimer of 
p-isopropenyl phenol having a purity of 98% and containing 85% by weight 
of 4-methyl-2,4-bis(4-hydroxyphenyl)-pent-1-ene and 15% by weight of 
4-methyl-2,4-bis(4-hydroxyphenyl)-pent-2-ene was used as a starting 
material. There was obtained 88.5 parts of the same linear trimer of 
p-isopropenyl phenol as obtained in Example 1. 
EXAMPLE 7 
Example 1 was repeated except that 0.5 part of a 10% aqueous solution of 
sulfuric acid was used instead of the 10% aqueous solution of hydrochloric 
acid. There was obtained 53 parts of the same linear trimer of 
p-isopropenyl phenol as obtained in Example 1. 
EXAMPLE 8 
A glass reactor was charged with 50 parts of benzene and 100 parts of a 
linear dimer of p-isopropenyl phenol having a purity of 98% and containing 
85% by weight of 4-methyl-2,4-bis(4-hydroxyphenyl)-pent-1-ene and 15% by 
weight of 4-methyl-2,4-bis(4-hydroxyphenyl)-pent-2-ene, and they were 
maintained at 50.degree. C. Separately, a 5% carbon tetrachloride solution 
of a boron trifluoride - ether complex was prepared, and 0.5 part of the 
solution was fed into the reactor. The reaction was performed at 
50.degree. C. for 4 hours. There was obtained 65 parts of the same linear 
trimer of p-isopropenyl phenol as obtained in Example 1. 
EXAMPLE 9 
A glass reactor was charged with 100 parts of monomeric p-isopropenyl 
phenol having a purity of 99.5% and 500 parts of benzene, and with 
stirring at 10.degree. C., 2.5 parts of p-toluenesulfonic acid was added. 
After exotherm subsided, the reaction was performed at 35.degree. C. for 3 
hours. The crystals that precipitated were separated by filtration, and 
dried. This product was determined to be the same compound as the linear 
trimer obtained in Example 1 as a result of its gas chromatographic 
analysis, infrared absorption spectrum analysis and high-speed liquid 
chromatographic analysis. The yield of the product was 81.5 parts. 
EXAMPLE 10 
Example 1 was repeated except that the amount of the 10% aqueous solution 
of hydrochloric acid was changed to 5 parts, and the reaction was 
performed at 70.degree. C. for 1 hour. There was obtained 58 parts of a 
linear trimer of p-isopropenyl phenol of formula [I]. It was confirmed by 
its gas chromatographic analysis and nuclear magnetic resonance spectrum 
that this linear trimer is a mixture of 87% of the trans-isomer and 13% of 
the cis-isomer. Repeated fractional crystallization of this mixture using 
benzene afforded a substantially pure trans-isomer (m.p. 
167.degree.-168.degree. C.). The chemical shifts (.delta. values) of the 
nuclear magnetic resonance spectrum of the trans-isomer (in 
acetone-D.sub.6) were as follows: 
______________________________________ 
--CH.sub.3 1.04, 1.13 ppm 
--CH.sub.2 -- 2.68 
.dbd.CH-- 5.53 
--.phi.--OH 8.00 
______________________________________ 
The infrared absorption spectrum of this trans-isomer is shown in FIG. 2. 
EXAMPLE 11 
A glass reactor was charged with 50 parts of a linear dimer of 
p-isopropenyl phenol (purity 98%) and 30 parts of nitrobenzene, and they 
were maintained at 60.degree. C. Then, 0.5 part of activated clay was 
added as an acid catalyst to the reaction system, and with stirring at 
60.degree. C., the reaction was performed for 8 hours. The product was not 
seen to precipitate from the reaction mixture. 
A gas chromatographic analysis of the reaction mixture showed the formation 
of the following compounds (the amounts in % are based on the total amount 
of the dimer of p-isopropenyl phenol charged). 
______________________________________ 
Compounds Amounts (%) 
______________________________________ 
Linear trimer (trans-isomer) 
of formula [I] 43% 
Linear trimer (cis-isomer) 
of formula [I] 21% 
Cyclic dimer of p-isopropenyl phenol 
17% 
Linear dimer (unreacted) of 
p-isopropenyl phenol 12% 
Monomer of p-isopropenyl phenol 
1% 
Tetramer and higher polymers of 
p-isopropenyl phenol 6% 
______________________________________ 
The reaction mixture was filtered to separate the activated clay. By adding 
110 parts of benzene to the filtrate, a white precipitate was formed. The 
precipitate was separated by filtration, washed, and dried to form 23 
parts of a linear trimer of p-isopropenyl phenol of formula [I] consisting 
of 62% of the trans-isomer and 38% of the cis-isomer. 
EXAMPLE 12 
A glass reactor was charged with 100 parts of the same mixture of linear 
polymers of p-isopropenyl phenol as used in Example 1 and 200 parts of 
dioxane, and they were maintained at 40.degree. C. Then, 1 part of a 10% 
aqueous solution of sulfuric acid was added, and the reaction was 
performed at 40.degree. C. for 6 hours. The reaction mixture was a uniform 
solution and the reaction product was not seen to precipitate. 
The reaction mixture was neutralized with an aqueous solution of sodium 
hydroxide, and then distilled under reduced pressure to distill off 150 
parts of the dioxane. To the remaining solution was added 100 parts of 
benzene to form a white precipitate. The precipitate was collected by 
filtration, washed, and dried to afford 42 parts of a powdery solid. By a 
gas-chromatographic analysis, this solid was found to be a linear trimer 
of p-isopropenyl phenol of formula [I] consisting of 25% of the 
trans-isomer and 75% of the cis-isomer.