Process for purification of p-isopropyl phenol

A process for purifying p-isopropyl phenol (PIPP) by distilling the impure phenol at a pot temperature below about 475.degree. F. under sufficient vacuum to permit separation of a heart cut, and washing the separated heart cut with liquid hydrocarbon containing from about 5 to about 10 carbon atoms.

p-Isopropyl phenol (PIPP) is a useful chemical intermediate for the organic 
synthesis of insecticides, anti-oxidants and pharmaceuticals. A source of 
PIPP is as a by-product in the production of hydroquinone where 
1,4-diisopropylbenzene is oxidized. Because there is no efficient and 
economical means to obtain purified PIPP from the oxidation reaction mass 
containing numerous by-products, it has been common practice to separate 
the desired hydroquinone and dispose of the PIPP and other by-products 
present by burning or other wasteful means. 
This invention now provides means to obtain high purity PIPP from its 
admixture with other materials, particularly with those by-products formed 
by oxidation of 1,4-disopropylbenzene to hydroquinone. In accord with the 
invention PIPP is produced in purified form by distilling the impure 
material at a pot temperature below 475.degree. F. and under sufficient 
vacuum to distill over a heart cut at temperatures corresponding to about 
410.degree. to about 466.degree. F. at 760 mm pressure and washing the 
heart cut with a low molecular weight hydrocarbon, i.e., a liquid 
hydrocarbon containing from about five to about ten carbon atoms. 
As indicated, the process is of particular advantage for the separation of 
purified PIPP from its admixture with the by-products of 
1,4-diisopropylbenzene oxidation. Normally such a mixture will contain 
about 60% to 65% by weight of PIPP. In accord with the process of the 
invention, this mixture is distilled under vacuum in conventional 
distillation equipment, a packed column being quite suitable. When the 
temperature rises and remains level, the desired fraction is separated, 
the distillation being carried out under sufficient vacuum to maintain the 
pot temperature below 475.degree. F. in order to avoid decomposition of 
the PIPP to phenol and other materials. 
It will be understood that the temperature at which the heart cut is taken 
will depend upon the pressure of the distillation. Thus, for example when 
distilling at 100 mm Hg. pressure, the temperature will level off at about 
284.degree. F. and distillation of the heart cut may continue to about 
334.degree. F. At a pressure of 180 mm, the heart cut fraction is taken 
from about 317.degree. F. to 368.degree. F. Thus, as is understood in the 
art the equivalent distillation temperature at 760 mm pressure will be 
about 410.degree. to about 466.degree. F. 
The distillate fraction obtained in this way contains PIPP in about 90% to 
96% purity and melts over a range of 48.degree. to 57.degree. C. Yield is 
about 50% to 60% PIPP. This still very impure fraction is then washed with 
a liquid aliphatic hydrocarbon. The liquid hydrocarbon will be one 
containing from about five to about ten carbon atoms and will be used at 
about room temperature or colder, preferably at about 5.degree. to about 
50.degree. F. The isomeric pentanes, and hexanes are particularly suitable 
hydrocarbons. A single wash will increase the PIPP purity to about 98% 
PIPP purity and additional n-pentane washings may be used to obtain higher 
purity. 
In order to further illustrate the invention the following examples are 
given:

EXAMPLE 1 
A crude PIPP mixture obtained from the oxidation of p-isopropylbenzene 
containing 62.5% PIPP by weight was distilled in a packed column with 40 
plates at 180 mm Hg. A heart cut fraction was taken over a boiling range 
of 317.degree. F. to 368.degree. F. This distillate contained 82% PIPP 
having a purity of 92% (m.p. 48.degree.-57.degree. C.). The distillate was 
washed once with 40 volume percent of cold n-pentane (45.degree. F.) to 
yield a solid product of 98.3% purity (m.p. 57.degree.-62.degree. C.). 
Recovery of PIPP from the heart cut was 90% and 74% from the crude 
starting material. Two additional n-pentane washes yielded PIPP of 99.9% 
purity. 
EXAMPLE 2 
A crude PIPP mixture from the oxidation of p-isopropylbenzene containing 
62% by weight of PIPP was distilled in a 40 plate packed column run at 20 
plates at a reflux ratio of 5:1 and at 100 mm Hg. The forecut taken at 
temperatures up to 284.degree. F. contained only 0.4% PIPP while the heart 
cut at 284.degree. to 334.degree. F. contained 84% PIPP at 87.3% purity. 
The heart cut was washed with 40 volume of mixed pentanes at 75.degree. F. 
to yield a 77.2% recovery of PIPP having 98.5% purity (m.p. 61.5.degree. 
F.). 
EXAMPLE 3 
When the details of Example 1 were repeated, but using a mixture of hexanes 
as the washing liquid, similar purification of the PIPP was obtained. 
As is evident from the above, the process of the invention yields a high 
purity PIPP product not easily obtainable heretofore. Although 
distillation of phenols is, of course, known in the art, the product of a 
PIPP distillation has heretofore been limited to a purity of about 96% or 
less, probably due to impurities which were always codistilled. The 
present invention provides an economical means to recover high purity PIPP 
from hydroquinone manufacture and thus is a valuable advance to the art.