Method of producing 2,3,6 trimethylphenol

A method is provided for producing 2,3,6 trimethylphenol by rearrangement of 2,4,6 trimethylphenol in the presence of an aluminum based catalyst, such as AlCl.sub.3, and an acid upon heating the mixture to a temperature within the range of 80.degree. C. to 150.degree. C.

BACKGROUND OF THE INVENTION 
This invention relates to a method of producing intermediate structures 
from the rearrangement of alkylated phenols in the presence of an aluminum 
based catalyst. More particularly, this invention relates to the 
rearrangment of 2,4,6 trimethylphenol to provide 2,3,6-trimethylphenol in 
the presence of an aluminum based catalyst. 
The ability to rearrange certain alkylated phenols, other than 2,4,6 
trimethylphenol, in the presence of excess aluminum chloride has been 
disclosed by Baddeley, J. CHEM. SOC. Vol. 994, pp. 527-531 (1950). 
Baddeley does not achieve complete rearrangement of all the starting 
material in his process. The starting materials remain in equilibrium with 
the finished products, making the product yields low. 
Fury and Pearson, J. Org. Chem. Vol. 30, pp. 2301-2304 (1965), disclose 
that complete rearrangment of the alkylated phenol starting material can 
be achieved by introducing anhydrous hydrogen chloride to the reaction 
medium with excess aluminum chloride. However, they do not obtain 
desirable reaction intermediates as finished products in the process they 
disclose. For example, Fury and Pearson disclose that the only product 
obtained upon rearrangement of 2,4,6 trimethylphenol is 2,3,5 
trimethylphenol. They do not obtain 2,3,6 trimethylphenol from the 
rearrangment of 2,4,6 trimethylphenol and they do not indicate that such a 
product can be obtained. 
This invention is based on the discovery that intermediate structures, such 
as 2,3,6 trimethylphenol, are produced in the rearrangement of certain 
methylated phenols, such as 2,4,6 trimethylphenol, and that these 
intermediate structures can be isolated from the reaction medium in high 
yields by controlling the rate of the rearrangement reaction. It has also 
been discovered that anhydrous hydrogen chloride need not be added to the 
reaction medium to obtain complete conversion of starting materials and 
high yields of intermediates where the reaction vessel is maintained under 
pressure and an acid generating catalyst is used. 
SUMMARY OF THE INVENTION 
The method of producing 2,3,6 trimethylphenol is provided by heating 2,4,6 
trimethylphenol in the presence of of an aluminum based catalyst at a 
temperature in the range of about 80.degree. C. to about 150.degree. C. 
under pressure. Where the aluminum based catalyst is an organometallic 
catalyst, an anhydrous protonic acid is added to the reaction medium. 
OBJECTS OF THE INVENTION 
An object of the present invention is to produce 2,3,6 trimethylphenol in 
high yields with little or no by-product. 
Another object of the present invention is to rearrange 2,4,6 
trimethylphenol to a more useful compound. 
Another object of the present invention is to rearrange substantially all 
of an alkylated phenol in the presence of an aluminum halide catalyst 
without the addition of anhydrous hydrogen chloride or other protonic acid 
to the reaction medium. 
STATEMENT OF THE INVENTION 
These objects and other objects of this invention are accomplished by 
introducing an anhydrous aluminum based catalyst preferably to a quantity 
of 2,4,6 trimethylphenol (2,4,6-TMP), the molar quantity of anhydrous 
aluminum based catalyst being equal to or greater than the number of moles 
of 2,4,6 trimethylphenol. The reaction mixture is then heated to the 
desired reaction temperature and the pressure is maintained at the desired 
value to obtain 2,3,6 trimethylphenol (2,3,6-TMP). The reaction will also 
produce a quantity of 2,3,5 trimethylphenol (2,3,5-TMP) from the 2,3,6 
trimethylphenol initially produced. Essentially two rearrangements can 
occur within the reaction mixture. 
##STR1## 
There is no equilibrium obtained for the rearrangement of 2,3,6 
trimethylphenol to 2,3,5 trimethylphenol. To obtain any 2,3,6 
trimethylphenol from the reaction mixture described above, the reaction 
must be interrupted before all the 2,4,6 trimethylphenol is converted to 
2,3,5 trimethylphenol. 
To obtain high yields of 2,3,6 trimethylphenol, the time at which the 
reaction must be interrupted is dependent upon the rate of rearrangement 
in the reaction mixture. The rate of reaction is dependent on factors such 
as, for example, the quantity of aluminum based catalyst, the quantity of 
anhydrous protonic acid which is dissolved in the reaction mixture, the 
concentration of 2,4,6 trimethylphenol starting material, the reaction 
temperature, the type of aluminum based catalyst utilized, the type of 
anhydrous protonic acid dissolved in the reaction mixture, etc. 
To avoid complete conversion to 2,3,5-TMP the reaction should not continue 
beyond twenty four hours, even at very low reaction temperatures 
(80.degree. C.). The preferred duration of the reaction is actually less 
than three hours. After three hours within the most preferred temperature 
range (120.degree. C.-130.degree. C.), all the 2,4,6 trimethylphenol has 
typically rearranged and the 2,3,6 trimethylphenol produced has been 
slowly rearranging to 2,3,5 trimethylphenol for most of this time. Under 
conditions which favor high rates of rearrangement, the conversion of 
2,4,6 trimethylphenol to 2,3,6 trimethylphenol is complete within minutes. 
The production of 2,3,6 trimethylphenol is believed to begin 
instantaneously under conditions conducive to rearrangement and once 
produced, a portion of the 2,3,6 trimethylphenol begins to rearrange to 
2,3,5 trimethylphenol immediately. 
The term "aluminum based catalyst" as used herein is intended to describe 
and include the members of a group of catalysts consisting of aluminum 
halide catalysts, AlX.sub.3, such as aluminum chloride, aluminum bromide 
and aluminum iodide and the organometallic catalysts of the formula 
RAlX.sub.2, wherein X is a halogen from the group consisting of chlorine, 
bromine and iodine and R is a monovalent organic radical selected from the 
group consisting of alkyl radicals of from 1 to 20 carbon atoms and 
aromatic radicals of from 6 to 20 carbon atoms. The term "aluminum based 
catalyst" is also intended to describe and include mixtures of the 
catalysts in the group described above. 
For the aluminum based catalysts to function, they must be in the presence 
of an anhydrous protonic acid. The aluminum halide catalysts will provide 
rearrangement of 2,4,6 trimethylphenol without the addition of an 
anhydrous protonic acid since such an acid is generated in the reaction 
mixture upon the addition of the aluminum halide catalyst to the 2,4,6 
trimethylphenol in accordance with the following equation. 
##STR2## 
The reaction mixture must be maintained under pressure to prevent the acid 
from escaping. 
The organometallic catalysts of the formula RAlX.sub.2 require the addition 
of an anhydrous protonic acid to the reaction mixture to achieve 
rearrangement of 2,4,6 trimethylphenol since an acid is not generated upon 
reaction of the organometallic catalyst and the 2,4,6 trimethylphenol. 
##STR3## 
Instead the reaction provides an organic compound from the monovalent 
organic radical that dissociates from the organometallic catalyst. 
The term "protonic acid" as used herein is intended to describe hydrogen 
compounds which dissociate in water and provide a free proton, H.sup.+ or 
H.sub.3.sup.+ O. Essentially any protonic acid is suitable for activating 
the aluminum based catalysts utilized in this invention to provide 
rearrangement of 2,4,6 trimethylphenol. However, some of these acids may 
react with the 2,4,6 trimethylphenol and produce an unwanted derivative. 
For example, sulfuric acid can cause the addition of a sulfonate radical 
to the 2,4,6 trimethylphenol and nitric acid can cause the nitration of 
2,4,6 trimethylphenol. 
Protonic acids that are preferred for addition to the reaction medium are 
those that are generated by the reaction of aluminum halide catalyst and 
the 2,4,6 trimethylphenol. These include, hydrogen chloride, hydrogen 
bromide and hydrogen iodide. Other protonic acids which are suitable 
include the following: 
HF--Hydrogen fluoride 
HClO.sub.4 --Perchloric 
HClO.sub.3 --Chloric 
HClO.sub.2 --Chlorous 
HClO--Hypochlorous 
HBrO.sub.3 --Bromic 
H.sub.2 CO.sub.3 --Carbonic 
H.sub.3 PO.sub.2 --Hypophosphorous 
H.sub.3 PO.sub.3 --Phosphorous 
H.sub.3 PO.sub.4 --Phosphoric 
Carboxylic acids are also suitable such as, for example, acetic acid, 
formic acid, propanoic acid, butanoic acid, 2-methyl propanoic acid, 
pentanoic acid, chloroacetic acid, trichloroacetic acid, trifluoroacetic 
acid, stearic acid, benzoic acid, phenyl acetic acid, 
2-chlorobutanoic,3-chlorobutanoic dichloroacetic acid, palmitic acid, 
4-chlorobutanoic acid, 5-chlorobutanoic acid, etc. 
To obtain a significant degree of rearrangement, it is preferable to 
utilize a molar quantity of aluminum based catalyst which exceeds the 
molar quantity of 2,4,6 trimethylphenol. Where the quantity of catalyst 
falls below 1 molar equivalent of 2,4,6 trimethylphenol, negligible 
rearrangement occurs even at preferred reaction temperatures over 
relatively long reaction times. 
Not wishing to be bound by theory, it is believed that one equivalent of 
the aluminum based catalyst is necessary to react with the hydroxyl group 
of the 2,4,6 trimethylphenol and provide the species in which 
rearrangement takes place, as illustrated in Equations III and IV. The 
quantity of catalyst which falls above 1 molar equivalent of 2,4,6 
trimethylphenol is then free to initiate rearrangement. The quantity of 
catalyst above 1 molar equivalent is believed to form a complex with the 
anhydrous protonic acid generated or introduced into the reaction medium 
in accordance with the following equations: 
EQU RAlX.sub.2 +2(H-Z).fwdarw.R-H+HAlX.sub.2 Z.sub.2 V 
EQU AlX.sub.3 +H-Z.fwdarw.HAlX.sub.3 Z 
wherein X is selected from a group consisting of chlorine, bromine and 
iodine, R is an organic radical as previously defined and Z is the 
conjugate base of a suitable protonic acid. It is believed these complexes 
(Lewis acids) provide a proton which rearranges the methyl groups on the 
2,4,6 trimethylphenol. 
The preferred quantity of catalyst falls in the range of one to two moles 
per mole of 2,4,6 trimethylphenol. Only a trace quantity of aluminum based 
catalyst above 1 molar equivalent of 2,4,6 TMP is necessary to obtain a 
high rate of rearrangement. Quantities of catalyst larger than 2 molar 
equivalents of 2,4,6 trimethylphenol can be utilized; however, the rate of 
rearrangement is very high and the quantity of 2,3,5 trimethylphenol 
produced is very large. 
Where an anhydrous protonic acid is to be added to the reaction medium and 
it is a gas at the reaction temperature, it is either bubbled through the 
reaction mixture or the reaction mixture is maintained under a fixed 
pressure of the protonic acid gas. Maintaining the reaction medium under 
pressure of the anhydrous protonic acid is preferred since a smaller 
quantity of acid can be used and this quantity can be monitored and 
controlled. 
It is preferable to maintain the pressure of the reaction medium within the 
range of about 5-70 psig to keep the protonic acid in solution. This range 
is preferred where the protonic acid is generated in the reaction medium 
and where it is introduced. Where the protonic acid is generated in the 
reaction medium, the pressures may be generated by another gas so long as 
the protonic acid remains in solution. Where excessive acid is produced, 
the gaseous anhydrous acid may be released to maintain the pressure 
desired. 
Although a protonic acid is generated within the reaction mixture upon 
addition of an aluminum halide catalyst, additional amounts of acid may be 
introduced if higher pressures are desired to maintain more acid in 
solution. 
The use of pressures of anhydrous protonic acid above 30 psig are preferred 
over those below 30 psig since the rate of rearrangement is relatively 
low. However, quantities above 70 psig of anhydrous protonic acid 
acclerate the rearrangement reaction and produce large quantities of 2,3,5 
trimethylphenol. Although these high pressures can be utilized, they are 
not preferred for the production of 2,3,6 trimethylphenol. 
The temperature of the reaction mixture during rearrangement is preferably 
maintained within the range of about 80.degree. C. to about 150.degree. C. 
Temperatures higher than 150.degree. C. produce larger quantities of 2,3,5 
trimethylphenol than is desirable due to a higher rate of rearrangement. 
At temperatures below 80.degree. C., the rate of 2,4,6 trimethylphenol 
rearrangement is very low, even after extended periods of exposure to such 
temperatures. The most preferred temperatures fall in the range of about 
120.degree. C. to 130.degree. C. 
The rate of rearrangement can also be reduced by reducing the concentration 
of the reactants. This is accomplished by introducing a solvent to the 
reaction medium. Suitable solvents include any aprotic solvent such as, 
for example, chlorobenzene, benzene, toluene, dichlorobenzene, chloroform, 
etc. Solvents containing amino groups or hydroxy groups are unsuitable 
since they interfere with the catalyst. As indicated above, chlorinated 
hydrocarbon and unsubstituted hydrocarbon solvents are suitable. The 
concentration of 2,4,6 trimethylphenol in solvent can fall as low as 0.01 
moles per liter of solvent. Since the reaction can proceed in the absence 
of solvent, the upper limit of the concentration of 2,4,6 trimethylphenol 
in solvent approaches 100%. High yields of 2,3,6 trimethylphenol have been 
obtained where the 2,4,6 trimethylphenol is maintained at a concentration 
of one mole/liter of solvent and such a concentration is preferred over 
more dilute concentrations to avoid the use of large quantities of 
solvent. 
Once the reaction proceeds, the rearrangement is stopped by the addition of 
water to hydrolize the aluminum based catalyst. Where a solvent is 
utilized and the reaction conditions have been maintained in the preferred 
ranges discussed above, a reaction time of about 10 minutes is preferred. 
However, as discussed above, 2,3,6 trimethylphenol can be obtained at both 
longer and shorter reaction times. It has been found that yields of 2,3,6 
trimethylphenol suffer significantly after three hours when operating at 
the most preferred reaction conditions. 
The following examples are provided so that those skilled in the art may 
better understand this invention. It is not intended to limit the scope of 
the invention to the embodiments they describe.

EXAMPLES 1-9 
In each of examples 1-9, the following procedure was utilized. Details as 
to the reaction conditions and the reaction products for each of the 
examples is reported in Table I. 
A 200 ml. Fisher-Porter pressure bottle was charged with 2,4,6 
trimethylphenol and anhydrous AlCl.sub.3 in a quantity corresponding to 
that reported in Table I. The bottle was equipped with a pressure 
regulator and then charged with anhydrous hydrogen chloride to a pressure 
as specified in Table I for the particular example. No special precautions 
were taken to exclude atmospheric moisture. The vessel was then placed in 
oil bath at a temperature as indicated in Table I. The reaction mixture 
typically became homogeneous and acquired a red color. The reaction was 
maintained at the temperature specified in Table I and the rearrangement 
reaction was interrupted by pouring the reaction mixture over 300 ml. of 
ice water. The aqueous phase with precipitated product was extracted with 
methylene chloride. The combined methylene chloride abstract was washed 
with saturated aqueous sodium bicarbonate and then passed through a plug 
of glass wool. The methylene chloride was removed on a rotary evaporator 
to isolate the product. 
The weight percent of 2,4,6 trimethylphenol, 2,3,6 trimethylphenol, and 
2,3,5 trimethylphenol which appeared in the product are shown in Table I. 
TABLE I 
______________________________________ 
Rearrangement of 2,4,6 Trimethylphenol with AlCl.sub.3 and HCl 
Re- 
action Molar 
Exam- Temp Time equiv. 
HCl Products (wt. %) 
ple .degree.C. 
(min) AlCl.sub.3 
psig 2,4,6* 
2,3,6* 
2,3,5* 
______________________________________ 
1 124 180 2.0 50 1.5 1.3 97.2 
2 124 50 2.0 50 1.2 18.3 80.6 
3 124 10 2.0 50 1.4 38.1 59.5 
4 124 60 0.0 50 100.0 0.0 0.0 
5 120 60 0.75 50 70.9 9.0 10.3 
6 120 60 1.0 50 66.2 18.9 7.8 
7 80 60 2.0 50 37.9 39.7 18.0 
8 105 120 2.0 50 5.5 30.1 59.2 
9 110 45 2.0 50 3.7 53.6 37.1 
______________________________________ 
*Trimethylphenol 
Examples 1-3 illustrate the effect the reaction time has on the yield of 
2,3,6 trimethylphenol. All reaction conditions in these three examples 
were maintained the same except for the reaction time. Where the reaction 
time was three hours, the reaction product was essentially 2,3,5 
trimethylphenol. In Example 1, over 97% of the 2,4,6 trimethylphenol 
started with was rearranged to 2,3,5 trimethylphenol. Example 2 indicates 
how a reduction in reaction time substantially increases the yield of 
2,3,6 trimethylphenol. Example 3 indicates how short reaction times are 
essential in obtaining high yields of 2,3,6 trimethylphenol when operating 
in the most preferred temperature range. The yield of 2,3,6 
trimethylphenol was doubled by reducing the reaction time from 50 to 10 
minutes. 
Examples 4-6 demonstrate the importance of utilizing 1 mole of aluminum 
based catalyst. In Example 5, less than 1 molar equivalent of AlCl.sub.3 
was utilized and only 30% of the 2,4,6 trimethylphenol rearranged after 
one hour. Increasing the quantity of of AlCl.sub.3 to 1 mole per mole of 
2,4,6 trimethylphenol did not significantly enhance the rate of 
rearrangement, as shown in Example 6. 
Examples 7-9 illustrate the role that the reaction temperature plays in 
determining the rate of rearrangement. Only a portion of the 2,4,6 
trimethylphenol rearranged where the reaction temperature was maintained 
at 80.degree. C., even though the reaction was permitted to proceed for 
one hour. Examples 8 and 9 illustrate that high yields of 2,3,6 
trimethylphenol can be obtained for relatively long reaction times where 
lower reaction temperatures are utilized. For example, although the 
reaction was permitted to proceed for two hours in Example 8, a higher 
yield of 2,3,6 trimethylphenol was obtained over that of Example 2, which 
operated at 124.degree. C. Example 9 illustrates how the low temperatures 
and short reaction times can be utilized in concert to obtain high yields 
of 2,3,6 trimethylphenol. In this example, the highest yield of 2,3,6 
trimethylphenol was obtained. 
EXAMPLES 10-14 
In each of examples 10-14, the same procedure was followed as described in 
examples 1-9. All reaction parameters were kept relatively constant at 
values similar to those in examples 1-9 except the reaction time. All 
reaction times were below 50 minutes. Details as to the reaction 
parameters and the product yield for each example are reported in Table 
II. 
TABLE II 
__________________________________________________________________________ 
Rearrangement of 2,4,6 Trimethylphenol With AlCl.sub.3 and HCl 
Reaction 
Molar 
Temp Time Equiv. 
HCl Products wt. % 
Example 
.degree.C. 
(Min) AlCl.sub.3 
psig 
2,4,6* 
2,3,6* 
2,3,5* 
Others 
__________________________________________________________________________ 
10 110 15 2 45 21.9 
53.8 
23.4 
0.0 
11 110 15 2 50 3.2 57.4 
35.6 
1.1 
12 110 20 2 50 3.9 57.1 
36.8 
1.5 
13 110 25 2 50 6.6 52.7 
38.2 
1.9 
14 110 45 2 50 3.7 53.6 
37.1 
0.0 
__________________________________________________________________________ 
*Trimethylphenol 
EXAMPLES 15-23 
In each of examples 15-23, the same procedure was followed as described in 
examples 1-9 except that a solvent, dichlorobenzene, was added to the 
2,4,6 trimethylphenol starting material. The concentration of 2,4,6 
trimethylphenol for each of example 145-23 is specified in Table III along 
with all reaction parameters and product yields. 
TABLE III 
__________________________________________________________________________ 
Rearrangement of 2,4,6 Trimethylphenol in Chlorobenzene 
Molar 
Reaction 
Conc. of 
HCl 
equiv. 
Products wt % 
Example 
Temp .degree.C. 
Time (Min.) 
2,4,6*(Molarity) 
psig 
AlCl.sub.3 
2,4,6* 
2,3,6* 
2,3,5* 
Others 
__________________________________________________________________________ 
15 124 11.5 2.1 40 2.0 67.3 
23.7 
9.0 
-- 
16 130 25 2.1 45 1.5 4.5 54.9 
38.0 
2.6 
17 130 30 1.5 45 1.5 3.5 51.0 
43.4 
2.1 
18 100 30 2.0 42 2.0 3.5 51.0 
43.4 
2.2 
19 100 60 2.0 40 2.0 8.7 62.6 
28.0 
0.8 
20 85 60 2.0 35 1.5 49.4 
34.5 
15.7 
0.4 
21 85 180 2.0 35 1.5 12.1 
62.3 
25.6 
-- 
22 85 225 2.0 35 1.5 19.4 
56.4 
23.5 
0.7 
23 85 960 2.0 35 1.5 8.8 63.7 
26.8 
0.6 
__________________________________________________________________________ 
*Trimethylphenol 
EXAMPLE 24 
This example illustrates that a sufficient quantity of a protonic acid can 
be generated within the reactor so as not to require any additional acid. 
To a 10-gallon glass-lined reactor equipped with a reverse curve impeller, 
baffles and thermocouple probe were added in order 7.54 Kg 2,4,6 
trimethylphenol, 15.1 L chlorobenzene, and 11.31 Kg aluminum chloride. The 
reactor was sealed and heated in an oil bath. The pot temperature rose 
steadily to 120.degree. C. over 110 minutes, during which time six samples 
were collected and analyzed by introducing the sample to ice water, 
extracting the product and solvent with methylene chloride and distilling 
off the methylene chloride and chlorobenzene. No anhydrous protonic acid 
was introduced. In fact, anhydrous HCl was vented off the reaction vessel 
to maintain a pressure below 40 psig. The composition of each of the six 
samples analyzed is shown in Table IV. 
TABLE IV 
______________________________________ 
Rearrangement of 2,4,6 Trimethylphenol in Chlorobenzene 
without HCl 
Reaction Products wt % 
Sample 
Time (Min) 2,4,6* 2,3,6* 2,3,5* 
Others 
______________________________________ 
1 29 81.0 13.6 4.8 -- 
2 44 56.5 27.0 15.4 -- 
3 55 27.8 43.5 26.8 1.5 
4 70 12.8 48.5 36.6 2.0 
5 85 7.6 44.3 44.8 3.0 
6 110 6.0 37.9 54.0 3.0 
______________________________________ 
*Trimethylphenol 
EXAMPLE 25 
This example also illustrates that a protonic acid need not be introduced 
into a reaction mixture where an alumium halide catalyst is used. To a 200 
ml Fisher-Porter pressure bottle were added (100 gms) 2,4,6 
trimethylphenol and (50 gms) of anhydrous AlCl.sub.3. The bottle was 
equipped with a pressure regulator to monitor the pressure of HCl 
produced. No HCl was added. The vessel was placed in an oil bath and 
heated to 130.degree. C. A pressure of 60 psig was noted. The reaction was 
interrupted after 40 minutes by adding the reaction mixture to 300 ml of 
ice water. The product was extracted with methylene chloride which was 
evaporated off to isolate the product. The product comprised 34.0 weight 
percent 2,4,6 trimethylphenol, 37.1 weight percent 2,3,6 trimethylphenol 
and 26.8 weight percent 2.35 trimethylphenol with the remainder being 
byproducts. 
Although the above examples have shown various modifications of the present 
invention, further modifications are possible in light of the above 
techniques by one skilled in the art without departing from the scope and 
spirit of this invention.