Process for cleavage of unsaturated multi-cyclic ketones

A process for cleavage of unsaturated multi-cyclic ketones involves thermal cracking of the liquid ketone at elevated temperatures in the absence of water to produce cyclohexanone and a variety of other cleavage products. Para-toluenesulfonic acid and transition metal oxides are advantageously employed as catalysts.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to the preparation of cyclic organic 
compounds. In particular it relates to the thermal cleavage of unsaturated 
multi-cyclic ketones to produce cyclohexanone and other cleavage products 
including cyclohexene and cyclohexanol. 
2. Prior Art Statement 
References considered of particular pertinence are set forth below. 
a. U.S. Pat. No. 3,574,757 (Collier) describes a process for hydrolytic 
cleavage of unsaturated bicyclic ketones which involves contacting a 
substantially anhydrous ketone with superheated steam and caustic. 
Although the starting material in this case is free of water, steam is 
added to the reaction mixture; part of this steam is consumed in the 
reaction which produces cyclohexanone. By way of contrast, the process of 
our invention uses no water whatsoever, and is thus a thermal rather than 
a hydrolytic cleavage. The hydrolytic cleavage of, for example, 
2-(1-cyclohexenyl)cyclohexanone or 2-cyclohexylidenecyclohexanone proceeds 
in a manner such that one molecule of water reacts with one molecule of 
bicyclic ketone to yield two molecules of cyclohexanone. Surprisingly, it 
has now been found that cyclohexanone as well as other compounds are 
obtained when a thermal cleavage reaction in the absence of water is 
carried out according to the process of our invention. As in the 
hydrolytic cleavage reaction, the thermal cleavage reaction proceeds 
readily when the starting material is an essentially pure bicyclic ketone, 
or a mixture containing said bicyclic ketones such as the high boiling 
fraction obtained from the distillation of cyclohexanone and cyclohexanol. 
It is known that said high-boiling fractions contain a variety of 
multi-cyclic compounds such as 2-(1-cyclohexenyl)cyclohexanone, 
2-cyclohexylidenecyclohexanone, and various other mutli-cyclic oxygenated 
compounds arising as condensation products of cyclohexanone or 
cyclohexanol. Thus, the chemical reaction of our process is different from 
that of U.S. Pat. No. 3,574,757, even though some operating conditions may 
be somewhat similar. Other references such as German patent Nos. 927,688 
and 946,443, and Czech patent No. 95,459 describe variations of the 
hydrolytic cleavage process. 
b. Japanese Pat. No. 39-26965 describes a process for heat-treating of a 
mixture of multi-cyclic compounds containing unsaturated bicyclic ketones 
which involves heating the mixture in the presence of water and an 
inorganic acid catalyst at atmospheric pressure, and recovering 
cyclohexanone and cyclohexene from a portion of the mixture. By way of 
contrast, the process of our invention requires no water whatsoever and 
may be carried out without the use of a catalyst. Furthermore, it has been 
found that the addition of small amounts of water as low as three to four 
percent by weight of the starting material such as used in the examples of 
this reference gives significantly different results compared to 
conducting the cleavage reaction using a substantially dry starting 
material containing less than about one percent of water. Surprisingly, 
the cleavage reaction does not cease in the absence of water, but shifts 
from hydrolytic to thermal along with a corresponding shift in the amounts 
and percentages of cleavage products, especially cyclohexanone. 
Thus, the cited references do not, whether alone or in combination, teach, 
suggest, or make obvious our invention, since the reactions therein are 
concerned with hydrolytic cleavage rather than thermal cleavage as in our 
process. Furthermore, the referenced art does not lead a person of 
ordinary skill in the art to predict with any degree of certainty the 
consequences of not having water present; experimental effort is 
essential. 
SUMMARY OF THE INVENTION 
A primary object of the present invention is to provide an economical, yet 
efficient and efficacious process for the cleavage of multi-cyclic 
ketones, thereby obviating disadvantages inherent in processes of the 
prior art. 
This object is achieved by the provision of a process which comprises 
confining a substantially dry unsaturated multi-cyclic ketone at a 
temperature from about 150.degree. to 350.degree. C. under a pressure high 
enough to ensure that a liquid phase is present, and recovering the 
products therefrom by conventional distillation methods well known to 
those with skill in the art. For the purposes of this disclosure, the 
phrase "substantially dry" includes material containing up to about one 
percent by weight of water based on the weight of the multi-cyclic ketone 
or mixture thereof. The multi-cyclic ketone is advantageously employed as 
a component of a high-boiling fraction from the distillation of 
cyclohexanone and cyclohexanol. Especially beneficial results are obtained 
in the practice of the present invention if a bicyclic ketone, or mixture 
thereof (e.g., the high boiling fraction from the distillation of 
cyclohexanone and cyclohexanol, supra) is confined substantially at or 
above the vapor pressure of the bicyclic ketone or mixture thereof, 
respectively. 
Outstanding results are obtained in the practice of the present invention 
if para-toluenesulfonic acid is employed as a catalyst for the cleavage 
reaction. 
Outstanding results are also obtained in the practice of the present 
invention if a catalyst is employed in the form of (a) nickel 
oxide/molybdenum oxide on an inert support, or (b) cobalt oxide/molybdenum 
oxide on an inert support, or (c) a mixture comprising (a) and (b) in 
various proportions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For a more complete understanding of the present invention, including its 
primary object and benefits, reference should be made to the description 
of the preferred embodiments thereof, which is set forth in detail below. 
All percentages in the following examples are on a weight basis. 
EXAMPLE 1 
In each of a series of experimental runs, a liquid residue from the 
distillation of cyclohexanone and cyclohexanol having from about 10-40 
percent by weight of 2-(1-cyclohexenyl)cyclohexanone and 
2-cyclohexylidenecyclohexanone was placed in a completely sealed stainless 
steel reaction bomb and heated at a temperature between 150.degree. and 
350.degree. C. for a period of 1/2 to 6 hours. Each bomb was then rapidly 
cooled. No raw materials other than the liquid residue were required. 
Temperatures of 200.degree.-350.degree. C. and reaction times from 1 to 3 
hours are preferred ranges. Below a temperature of about 200.degree. C. 
and without a catalyst, the thermal cleavage reaction proceeds so slowly 
as to be impractical. Above about 350.degree. C., other thermal cleavage 
and pyrolysis reactions may begin to take place giving undesirable 
products. Within the stated range of temperature, the process of our 
invention proceeds readily and yields the stated products with a minimum 
of side reactions when the starting material is the high boiling fraction 
from the distillation of cyclohexanone and cyclohexanol. As should be 
readily apparent to those with skill in the art of chemical reactions, the 
reaction time is strongly dependent upon reaction temperature such that 
the reaction rate increases as temperature increases within the stated 
range. Pressure required to keep reactants at least partially in liquid 
phase is atmospheric up to about 500 psig depending upon temperature and 
reaction time. Preferably, the pressure is maintained substantially at or 
above the vapor pressure of the reaction mixture. After 30 minutes at 
320.degree. C., in a sealed vessel operating at the vapor pressure of its 
contents, a residue initially containing about 2 percent cyclohexanol 
yielded a reaction product containing 8 percent cyclohexanone, 6 percent 
cyclohexanol, and 8 percent cyclohexene. Products may be recovered as the 
reaction progresses or afterwards by conventional distillation methods. 
EXAMPLE 2 
In another series of experimental runs, one to two percent 
para-toluenesulfonic acid in the form of dry crystals was added to the 
liquid residue utilized as the starting material in Example 1, and the 
mixtures were shaken until the crystals were dissolved. These mixtures 
were placed in completely sealed stainless steel reaction bombs and heated 
at 150.degree.-300.degree. C. for 15-30 minutes. Each bomb was then 
rapidly cooled to room temperature. A range from 0.01 to five percent 
para-toluenesulfonic acid was employed with beneficial results. 
Temperatures of 200.degree.-300.degree. C. and reaction times up to 30 
minutes are preferred ranges. Pressure required to keep reactants mostly 
in liquid phase is 100-500 psig. Preferably the pressure is maintained 
substantially at or above the vapor pressure of the reaction mixture. 
Using 2 percent para-toluenesulfonic acid at 250.degree. C. for 20 minutes 
gave a yield of 15 percent cyclohexanone, 10 percent cyclohexanol and 15 
percent cyclohexene. Products may be recovered as the reaction progresses 
or afterwards by conventional methods. 
EXAMPLE 3 
In another series of experimental runs, pellets of catalyst of the type 
normally used in hydrotreating applications (see below) and the liquid 
residue employed in Example 1 as starting material were added to a stirred 
reactor and heated to 175.degree.-300.degree. C. over a period of 1/2 -2 
hours and then allowed to cool. The reactor was sealed and allowed to run 
at the vapor pressure of its contents. The amount of catalyst used, based 
on liquid residue, was 10-15 percent. Catalysts, which were individually 
employed in the non-sulfided form, were: 10-15 percent of (a) a 
nickel-molybdenum catalyst (present as 3.8 percent nickel oxide and 16.8 
percent molybdenum trioxide); (b) a cobalt-molybdenum catalyst (present as 
3 percent cobalt oxide and 15 percent molybdenum dioxide) based on weight 
of liquid residue. 
A range of 10-100,000 liquid residue to catalyst weight ratio is employed 
with beneficial results. Mixtures of the catalyst are also employed with 
beneficial results. Temperatures of 175.degree. -250.degree. C. and 
reaction times up to one hour are preferred ranges. Pressure may range 
from atmospheric up to 5000 psig. 
HT-100 nickel-molybdenum catalyst, which was obtained from Harshaw Chemical 
Company, produced about 12 percent cyclohexene, 6 percent cyclohexanone, 
and 2 percent cyclohexanol in 1 hour at 225.degree. C. HT-400 
cobalt-molybdenum catalyst, which was also obtained from Harshaw Chemical 
Company, produced about 12 percent of cyclohexene, 8 percent 
cyclohexanone, and 2 percent cyclohexanol in 1 hour at 200.degree. C. 
Liquid residue to catalyst weight ratio was 10 in both cases. 
EXAMPLE 4 
A sample of 95 percent pure 2-(1-cyclohexenyl)cyclohexanone containing no 
water was heated, without the addition of water or steam and without a 
catalyst, under its vapor pressure in a sealed vessel at 300.degree. C. 
for a period of one hour. Afterwards, the vessel and contents were rapidly 
cooled. The resulting mixture was analyzed by gas chromatography and found 
to be a complex mixture containing about 12 percent cyclohexanone and 2 
percent cyclohexene in addition to a number of other cleavage products 
amounting to about 75 percent of the mixture. Approximately 90 percent of 
the starting bicyclic ketone was cleaved during the process. 
EXAMPLE 5 
The following experiment was carried out for the purpose of comparing the 
hydrolytic cleavage reaction with the thermal cleavage reaction. 
A sample of the high-boiling fraction from the distillation of 
cyclohexanone and cyclohexanol containing about 20 percent of 
2-(1-cyclohexenyl)cyclohexanone and no water was placed in a pressure 
vessel. Another sample of the same high-boiling fraction but containing 4 
percent water based on the weight of the mixture was placed in a second 
pressure vessel. Both vessels were then placed in an oven and allowed to 
operate at their respective vapor pressures at 300.degree. C. for a period 
of one hour. Afterwards, the vessels were rapidly cooled and the contents 
of each was analyzed by gas chromatography. 
The sample which contained no water was found to contain 7 percent 
cyclohexanone, 2 percent cyclohexanol, and 1 percent cyclohexene after 
conducting the cleavage. About 34 percent of the original 
2-(1-cyclohexenyl)cyclohexanone was cleaved during the process. The amount 
of cyclohexanone corresponded to about 100 percent of the amount of 
bicyclic ketone cleaved thermally. 
The sample which contained 4 percent water was found to contain 13 percent 
cyclohexanone, 2 percent cyclohexanol, and 1 percent cyclohexene. About 58 
percent of the original 2-(1-cyclohexenyl)cyclohexanone was cleaved during 
the process. The amount of cyclohexanone corresponded to 108 percent of 
the amount of bicyclic ketone cleaved hyrolytically, which corresponds to 
theory for the hydrolytic cleavage reaction in this case. 
The present invention has been specified in detail with respect to certain 
preferred embodiments thereof. As is understood by those of skill in this 
art, variations and modifications in this detail may be effected without 
any departure from the spirit and scope of the present invention, which is 
defined in the hereto-appended claims.