Inhibiting the carbon-carbon double bond isomerization of substituted or unsubstituted hydrocarbon compounds

The carbon-carbon double bond isomerization of a substituted or an unsubstituted hydrocarbon compound having olefinic unsaturation in a less stable form to an isomer of said compound having olefinic unsaturation in a more stable form is inhibited by contacting with said compound having the more unstable form with an alkali metal salt of a di-, tri- or tetracarboxylic acid.

BACKGROUND OF THE INVENTION 
The invention relates to a method for inhibiting the carbon-carbon double 
bond isomerization of substituted or unsubstituted hydrocarbon compounds. 
In one aspect the invention relates to a method for inhibiting the 
carbon-carbon double bond isomerization of a mononitrile. In another 
aspect the invention relates to a process for producing unsaturated 
dinitriles employing the above-noted method for inhibiting the 
carbon-carbon double bond isomerization of a mononitrile. 
Isomerization reactions involving the carbon-carbon double bond 
rearrangement of a variety of substituted or unsubstituted hydrocarbon 
compounds are well known in the art. Isomerization reactions are 
frequently employed in a process to increase the overall production of a 
specific compound from a multicomponent feedstream as, for example, in a 
process for producing 2-butene from a feedstream comprising 1-butene and 
2-butene. However, there are other instances, as in the present invention, 
where it is desirable to inhibit an isomerization reaction. For example it 
is frequently desirable to store a certain compound having olefinic 
unsaturation in a less stable form as compared to an isomer of said 
compound having olefinic unsaturation in a more stable form; however, 
isomerization often occurs spontaneously, thus providing a mixture of 
isomers. Such a situation exists in the storage of 
5-methyl-5-hexenenitrile, for example, of which a portion will 
spontaneously isomerize to produce 5-methyl-4-hexenenitrile, the more 
stable isomer. Likewise it is desirable to inhibit the isomerization of a 
compound existing in a less stable form when said compound is being used 
as a reactant in a reaction and an isomer of said compound having a more 
stable form produces an undesirable product. Such a situation can exist 
when an olefinically unsaturated mononitrile such as, for example, 
acrylonitrile, an olefinic hydrocarbon reactant such as, for example, 
isobutylene and the reaction product of the unsaturated mononitrile and 
the olefinic hydrocarbon reactant, frequently referred to as a monoadduct, 
such as, for example, 5-methyl-5-hexenenitrile, produced by reacting 
acrylonitrile and isobutylene, are reacted in the presence of an aqueous 
diluent to produce an olefinically unsaturated dinitrile product 
frequently referred to as a diadduct, such as, for example, 
5-methylene-1,9-nonanedinitrile. This reaction is generally described in 
U.S. Pat. No. 3,985,786, issued to Charles A. Drake on Oct. 12, 1976. In 
the above-described reaction it is generally undesirable for the 
5-methyl-5-hexenenitrile to isomerize to 5-methyl-4-hexenenitrile during 
the reaction. Inhibitors suitable for use in the above-described reaction 
are disclosed in U.S. Pat. No. 4,001,294, issued to Charles A. Drake et al 
on Jan. 4, 1977. As described therein as little as 0.5 weight percent of 
5-methyl-4-hexenenitrile in the reaction mixture as described above will 
adversely affect the fiber-forming properties of polymers derived from the 
5-methylene-1,9-nonanedinitrile diadduct produced by the reaction. 
Therefore it is clear that the use of inhibitors is of particular 
importance such as, for example, in the storage of certain compounds and 
in carrying out certain reactions, and although some such inhibitors are 
presently known and recognized in the art, there is still a need for 
additional inhibitors and inhibitors having improved inhibiting 
properties. 
Accordingly, it is an object of the invention to inhibit the carbon-carbon 
double bond isomerization of a compound having olefinic unsaturation in a 
less stable form to a compound having olefinic unsaturation in a more 
stable form. 
Another object of the invention is to inhibit the carbon-carbon double bond 
isomerization of a monoadduct produced by reacting an olefinic hydrocarbon 
and an olefinically unsaturated mononitrile when said monoadduct is 
reacted with a mononitrile to produce a dinitrile. 
Another object of the invention is a carbon-carbon double bond 
isomerization inhibitor having little or no tendency to corrode equipment 
required in various processes employing said inhibitor. 
Still another object of the invention is a carbon-carbon double bond 
isomerization inhibitor having little or no tendency to corrode equipment 
when employed in reactions in which an aqueous diluent is used. 
Still another object of the invention is a carbon-carbon double bond 
isomerization inhibitor which is an effective inhibitor in concentrations 
substantially lower than the concentration generally required for prior 
art inhibitors. 
These and other objects of the invention will be apparent to those skilled 
in the art upon studying the specification and the appended claims. 
According to the invention an acyclic or an alicyclic substituted or 
unsubstituted hydrocarbon compound having 4 to 30 carbon atoms per 
molecule and having olefinic unsaturation in a less stable form is 
inhibited from isomerizing to produce a corresponding isomer having 
olefinic unsaturation in a more stable form by contacting the compound 
with an alkali metal salt of a di-, tri- or tetracarboxylic acid. The use 
of such alkali metal salts substantially precludes the carbon-carbon 
double bond isomerization of a wide variety of substituted and 
unsubstituted hydrocarbons even when employed in concentrations 
substantially lower than the concentrations generally required for prior 
art inhibitors. 
Further according to the invention, the presence of an alkali metal salt of 
a di-, tri- or tetracarboxylic acid in a reaction mixture containing at 
least one olefinic hydrocarbon reactant, at least one olefinically 
unsaturated mononitrile reactant, at least one monoadduct reaction product 
of an olefinic hydrocarbon compound and an olefinically unsaturated 
mononitrile compound in the presence of an aqueous diluent substantially 
inhibits the carbon-carbon double bond isomerization of the 
above-described monoadduct from a less stable form with respect to the 
olefinic unsaturation to a more stable form. In addition it has been found 
that such salts are essentially noncorrosive with respect to the materials 
generally used in a reactor and associated equipment suitable for carrying 
out the above process. 
DETAILED DESCRIPTION OF THE INVENTION 
The isomerization inhibitor according to the instant invention is at least 
one alkali metal salt of a di-, tri- or tetracarboxylic acid represented 
by the general formula MO.sub.2 C-R(CO.sub.2 Z).sub.n wherein n is an 
integer having a value of 1, 2 or 3; wherein M is selected from the group 
consisting of lithium, sodium, potassium, rubidium and cesium; wherein 
each Z is independently selected from the group consisting of hydrogen, 
lithium, sodium, potassium, rubidium and cesium; and wherein R is selected 
from the group consisting of a valence bond, a hydrocarbyl radical and a 
hydroxy substituted hydrocarbyl radical, each of the hydrocarbyl radical 
and the hydroxy substituted hydrocarbyl radical having from 1 to 8 carbon 
atoms and having a valence equal to n+1. A number of runs hereinafter 
described were carried out with potassium salt inhibitors, in particular 
potassium salts of aliphatic dicarboxylic acids. Examples of suitable 
potassium salts of aliphatic dicarboxylic acids include potassium oxalate, 
potassium malonate, potassium succinate, potassium glutarate, potassium 
adipate, potassium pimelate, potassium suberate, potassium azelate, 
potassium sebacate, potassium 2,3-dimethylbutanedioate, potassium 
2-methylbutanedioate, potassium 2-methylpropanedioate, potassium 
2-methylhexanedioate, potassium 2-ethyl-3-methylpentanedioate, potassium 
3,3-dimethylpentanedioate, and potassium 2,3-diethylbutanedioate. Mixtures 
of any two or more of the above compounds can also be employed if desired. 
Further examples of suitable alkali metal salt inhibitors within the scope 
of the invention include potassium hydrogen terephthalate, lithium 
hydrogen isophthalate, sodium hydrogen orthophthalate, potassium 
terephthalate, potassium isophthalate, sodium orthophthalate, sodium 
citrate, lithium oxalate, sodium oxalate, rubidium oxalate, cesium 
oxalate, sodium hydrogen oxalate, rubidium hydrogen oxalate, lithium 
malonate, sodium succinate, rubidium glutarate, cesium adipate, lithium 
pimelate, sodium suberate, rubidium azelate, cesium sebacate, lithium 
2,3-dimethylbutanedioate, sodium 2-methylhexanedioate, rubidium 
2-ethyl-2-methylpentanedioate, cesium 3,3-dimethylpentanedioate, lithium 
2,3-diethylbutanedioate, sodium hydrogen adipate, potassium hydrogen 
pimelate, rubidium hydrogen suberate, cesium hydrogen azelate, lithium 
propane 1,2,3-tricarboxylate, potassium propane 1,2,3-tricarboxylate, 
potassium citrate, lithium citrate, sodium dihydrogen citrate, potassium 
dihydrogen citrate, sodium hydrogen citrate, potassium hydrogen citrate, 
sodium dihydrogen propane 1,2,3-tricarboxylate, potassium dihydrogen 
propane 1,2,3-tricarboxylate, sodium cyclopentane 
1,2,3,4-tetracarboxylate, potassium cyclopentane 1,2,3,4-tetracarboxylate, 
cesium cyclopentane 1,2,3,4-tetracarboxylate, potassium trihydrogen 
cyclopentane 1,2,3,4-tetracarboxylate, potassium dihydrogen cyclopentane 
1,2,3,4-tetracarboxylate, potassium hydrogen cyclopentane 
1,2,3,4-tetracarboxylate and mixtures of any two or more such compounds, 
as well as mixtures of one or more of such compounds with one or more of 
the potassium salts of aliphatic dicarboxylic acids. 
The isomerization inhibitor additives of the present invention are believed 
to be effective generally for inhibiting or retarding the carbon-carbon 
double bond isomerization of acyclic or alicyclic substituted or 
unsubstituted hydrocarbon compounds of 4-30 carbon atoms per molecule and 
having olefinic unsaturation in a less stable form to olefinic 
unsaturation in a more stable form. As used herein, the term "less stable 
form" refers to olefinic unsaturation having a lower degree of alkylation 
than the "more stable form" which, correspondingly, refers to olefinic 
unsaturation having a higher degree of alkylation. The effect of the 
degree of alkylation at the carbon-carbon double bond on olefin isomer 
stability is discussed, for example, on pages 22 and 23 of Physical 
Organic Chemistry by Jack Hine, McGraw-Hill Book Co., Inc., New York 
(1956). 
By means of general formulas (I) and (II), the isomerization which is 
described above and which is inhibited or retarded by the additives of 
this invention can be illustrated as follows: 
##STR1## 
wherein each R' is independently selected from the group consisting of 
hydrogen, alkyl radicals of 1-10 carbon atoms, and substituted alkyl 
radicals (as defined below) of 1-10 carbon atoms and wherein the carbon 
atoms in the carbon-carbon double bond represented by C.sub.a .dbd.C.sub.b 
in formula (I) have fewer alkyl or substituted alkyl radicals attached 
thereto as compared to the carbon atoms in the carbon-carbon double bond 
represented by C.sub.g .dbd.C.sub.y in formula (II). Q and Q' are the same 
or different and are within the range of from 0 to 7. The subscript 
letters used to identify the carbon atoms in formulas (I) and (II) do not 
necesarily identify the same carbon atoms in both formulas, for example, 
C.sub.a in formula (I) is not necessarily C.sub.a in formula (II). A 
substituted alkyl radical as used herein is an alkyl radical in which at 
least one of the hydrogens of the alkyl radical is replaced with a 
substituent other than a hydrocarbyl radical. Such substituent can be 
selected from a wide variety of groups. Examples of such substituents 
include the following: 
##STR2## 
wherein R" is a hydrocarbyl radical of 1-10 carbon atoms. Furthermore, 
said substituent should be attached to a carbon atom which is at least two 
carbon atoms (inclusive of the substituent-bearing atom) removed from the 
nearest carbon atom of the olefinic double bond in the compound of general 
formula (I). This latter proviso is intended to exclude from consideration 
those starting compounds wherein the substituent could have a significant 
effect on the relative stability of the isomers apart from the degree of 
alkylation of said olefinic double bonds by virtue of its closeness to the 
olefinic double bond. 
With further reference to compounds of general formula (I), it is also 
within the scope of the instant invention that alkyl or substituted alkyl 
groups on carbon atoms a and y can be joined or combined to thus form a 
carbocyclic ring system incorporating carbon atoms a, b and y therein. 
Examples of suitable starting compounds of general formula I whose olefinic 
isomerization can be effectively inhibited or retarded by the additives 
according to the instant invention include 1-butene, 1-pentene, 1-hexene, 
1-octene, 1-triacontene, 3-methylcyclohexene, 3-ethylcyclooctene, 
5-methyl-5-hexenenitrile, 5-hexenal, 5-hexenol, 6-methoxy-1-hexene, 
6-decyloxy-1-hexene, 1-octen-7-one, 5-hexenoic acid, 
3-methyl-4-cyclooctenecarboxylic acid, methyl 5-hexenoate, decyl 
5-hexenoate, decyl 19-eicosenoate, 20-decyloxy-1-eicosene, 
3-heptyl-5-cyano-8-decyloxycyclododecene, and mixtures of any two or more 
thereof. 
It has also been found that the isomerization inhibitors of the present 
invention are particularly suitable for use in reactions involving the 
production of unsaturated nitriles, such as the reactions described in 
U.S. Pat. No. 3,985,786 noted above. In these reactions an olefinically 
unsaturated nitrile, an olefinic hydrocarbon and a monoadduct of an 
olefinic hydrocarbon and an olefinically unsaturated nitrile are reacted, 
preferably in the presence of water, to yield olefinically unsaturated 
dinitrile products having a greater number of carbon atoms than the 
unsaturated nitrile reactant. 
Any unsaturated mononitrile can be employed in the practice of this 
invention to produce a dinitrile provided the mononitrile contains a cyano 
group attached to a carbon atom adjacent and doubly bonded to a carbon 
atom which is attached to at least one hydrogen atom. Preferably the 
mononitrile reactant is free of acetylenic unsaturation and contains from 
1 to 2 nonconjugated olefinic carbon-carbon double bonds as the sole 
unsaturation, while the total number of carbon atoms in the mononitrile 
reactant is within the range of 3 to 18, more preferably within the range 
of 3 to 8. Illustrative unsaturated mononitrile reactants include those 
represented by the formula R'"CH.dbd.CR'"--CN wherein each R'" is 
independently selected from the group consisting of hydrogen and 
hydrocarbyl radicals. Preferably the hydrocarbyl radicals are selected 
from the group consisting of alkyl, cycloalkyl, and aryl hydrocarbyl 
radicals and combinations thereof, for example alkylcycloalkyl, 
cycloalkylalkyl, aralkyl and arylcycloalkyl radicals. Examples of 
unsaturated nitriles meeting the requirements of the above formula are 
acrylonitrile, methacrylonitrile, 2-decenenitrile, 
3-cyclohexyl-2-propenenitrile, 4-phenyl-2-butenenitrile, 
3(p-tolyl)-2-propenenitrile, 2-butenenitrile, 2-hexenenitrile, 
5-methyl-2-hexenenitrile, 4-methyl-2-heptenenitrile, 
6,6,8,8-tetramethyl-2-nonenenitrile, 6-cyclohexyl-2-octenenitrile, 
6-phenyl-2-decenenitrile, 2-octadecenenitrile, 
6,7,8-trimethyl-9-phenyl-2-nonenenitrile, and 5-p-tolyl-2-nonenenitrile 
and mixtures of any two or more thereof. 
Any acyclic or cyclic olefinic hydrocarbon compound can be employed to 
produce a monoadduct which is in turn employed to produce a diadduct 
according to the invention, provided that the compound has at least one 
allylic hydrogen atom and the doubly bonded carbon atoms are free of cyano 
groups. The olefinic hydrocarbons preferably are free of acetylenic 
unsaturation and have from 3 to 18 carbon atoms per molecule with from 1 
to 2 nonconjugated olefinic carbon-carbon double bonds as the sole 
unsaturation. The preferred types of these compounds are the open chain 
monoolefinic hydrocarbons represented by the formula R.sup.IV.sub.2 
C.dbd.CR.sup.IV --CHR.sup.IV.sub.2, wherein each R.sup.IV is independently 
selected from the group consisting of hydrogen and hydrocarbyl radicals, 
said hydrocarbyl radicals being selected from the group consisting of 
alkyl, cycloalkyl, and aryl hydrocarbyl radicals and combinations thereof. 
Especially preferred are those monoolefinic hydrocarbons having 3 to 12 
carbon atoms and having an alkyl group, preferably methyl, as a side chain 
attached to at least one of the carbon atoms comprising the carbon-carbon 
double bond. Specific examples of olefinically unsaturated hydrocarbon 
compounds which are useful in the process of this invention include 
propylene, isobutylene, diisobutylene, triisobutylene, 1,5-hexadiene, 
beta-pinene, 1,5-cyclooctadiene, 2,4,4-trimethyl-1-pentene, 2-butene, 
biallyl, bimethallyl, alpha-methylstyrene, beta-methylstyrene, 1-pentene, 
1-decene, cyclohexene, 1-allylcyclohexene, 3-allylcyclohexene, 
4-allylcyclohexene, allylbenzene, 3,4,4-trimethyl-2-pentene, 1-dodecene, 
2,3-dimethyl-2-butene, and 2-methyl-1-phenyl-2-propene, and mixtures of 
any two or more thereof. 
Suitable monoadducts include any monoadduct reaction product of an olefinic 
hydrocarbon, as hereinabove defined, and an unsaturated mononitrile, as 
hereinabove defined. It is currently believed that the olefinic 
hydrocarbon compound and the unsaturated mononitrile react in accordance 
with the "ene" reaction to produce, as the principal monoadduct reaction 
product, a compound having the structural formula 
##STR3## 
Generally, a lesser amount of an isomeric monoadduct reaction product 
having the formula 
##STR4## 
is also produced. R"' and R.sup.IV are as defined above for the 
unsaturated mononitrile and the open chain monoolefinic hydrocarbon. 
As used herein the "ene" reaction is the addition of a compound with a 
double bond (enophile) to an olefin possessing an allylic hydrogen (ene) 
and involves allylic shift of one double bond, transfer of the allylic 
hydrogen to the enophile and bonding between the two unsaturated termini. 
Examples of suitable monoadduct reactants include 5-methyl-5-hexenenitrile, 
3,5-dimethyl-5-hexenenitrile, 3-(n-propyl)-5-hexenenitrile, 
3-(n-propyl)-6-phenyl-5-hexenenitrile, 2,4-dimethyl-4-pentenenitrile, 
2-ethyl-4-methyl-4-pentenenitrile, 2-(n-butyl)-4-pentenenitrile, 
2-(n-butyl)-5-phenyl-4-pentenenitrile, and mixtures of any two or more 
thereof. 
The diadduct reaction products, i.e. the dinitriles, obtained by the 
process of this invention comprise the reaction product mixtures formed by 
the monoaddition of an unsaturated mononitrile and any monoadduct reaction 
product. Exemplary of a diadduct reaction product is the reaction product 
mixture consisting of the major isomer species 5-methylenenonanedinitrile 
and 5-methyl-4-nonenedinitrile, and minor isomer species 
2-methyl-4-methyleneoctanedinitrile, 2,4-dimethyl-4-octenedinitrile, 
2,4-dimethyl-3-octenedinitrile, 2,6-dimethyl-4-methyleneheptanedinitrile 
and 2,4,6-trimethyl-3-heptenedinitrile. 
The amount of inhibitor utilized according to the instant invention can be 
conveniently expressed in terms of the weight percent of inhibitor added 
based on the amount of less stable isomer. The amount of inhibitor 
employed can be selected over a rather wide range but will broadly be in 
the range of about 0.0001 to about 10% by weight; however, based upon the 
results of the runs described herein the amount of inhibitor employed will 
preferably be within a range of from about 0.0005 to about 2% by weight 
based on the less stable isomer. In the specific process under discussion 
the amount of inhibitor employed is based upon the weight of monoadduct 
reaction product described above. 
In a continuous reaction process, the isomerization inhibitor of the 
instant invention is often conveniently added as a dispersion or solution 
of the inhibitor in water. In a batch process, which is less preferred, 
the charge order of reactants including the inhibitor dispersed or 
dissolved in water is not critical and any convenient charge order can be 
employed. 
The effluent from the reaction zone in either a batch or continuous 
reaction process can be treated by conventional separation procedures and 
the aqueous phase separated and recycled as desired to the reaction zone. 
It will be readily apparent that such recycle of the aqueous phase will, 
in many instances, provide for recycle of at least a portion of the 
inhibitor originally charged to the reaction zone. The amount of said 
inhibitor being recycled to the reaction zone in the recycled aqueous 
phase can be conveniently determined by conventional analytical 
techniques. Allowance for the amount of isomerization inhibitor being 
recycled can then be made when charging additional inhibitor to the 
reaction zone. 
Any amount of olefinic hydrocarbon, olefinically unsaturated mononitrile 
and monoadduct reaction product can be employed in the practice of this 
invention. In general the mol ratio of olefinically unsaturated 
mononitrile reactant to olefinic hydrocarbon reactant will be in the range 
of about 10:1 to about 0.1:1. Frequently the mol ratio of olefinically 
unsaturated mononitrile reactant to olefinic hydrocarbon reactant is in 
the range of about 5:1 to about 0.2:1; however, based upon the results of 
the runs hereinafter described it is believed that the ratio can be within 
the range of about 2:1 to about 0.3:1. In general the monoadduct reaction 
product is employed in an amount such that during substantially the entire 
reaction period the net monoadduct reaction product present in the 
reaction mixture will constitute from about 10 to about 90 weight percent 
of the total reaction mixture. Frequently the reaction is carried out such 
that the net monoadduct reaction product present in the reaction mixture 
is in the range from about 20 to about 80, and more often from about 30 to 
about 70 weight percent of the total reaction mixture. As used herein the 
term "net amount of monoadduct reaction product present in the reaction 
zone" is the sum of the amount of monoadduct reaction product charged to 
the reaction zone plus the amount of monoadduct reaction product produced 
by the reaction of the olefinic hydrocarbon reactant and the olefinically 
unsaturated mononitrile reactant in the reaction zone less the monoadduct 
reaction product consumed by reaction with the olefinically unsaturated 
mononitrile in the reaction zone to produce diadduct. The monoadduct 
reaction product charged to the reaction zone can be the same as or 
different from the monoadduct reaction product produced by the reaction of 
the olefinic hydrocarbon reactant and the olefinically unsaturated 
mononitrile reactant in the reaction zone, but it is generally preferred 
for them to be the same. The total reaction mixture includes all fluid 
materials present in the reaction zone, i.e. reactants, diluents, 
products, byproducts, etc. 
Any suitable reaction conditions for either a batch process or a continuous 
process can be employed in the practice of the invention. The reaction 
time employed in the practice of this invention can vary widely. Generally 
a time period of from about two minutes to about 48 hours is used; 
however, a time period ranging from about 30 minutes to about 10 hours can 
also be used. The results of the runs herein indicate that the time period 
can be within the range of from about 1 hour to about 5 hours for the 
olefin, unsaturated mononitrile and the monoadduct reaction product to be 
suitably admixed in the preparation of reaction products in high yields in 
a batch process. In a continuous process the liquid hourly space velocity 
will generally be in the range of about 0.05 to about 20, preferably in 
the range of about 0.1 to about 10, more preferably in the range of about 
0.5 to about 2. 
The reaction temperatures that can be employed in the practice of the 
invention can be selected over a wide range. Generally, however, suitable 
reaction temperatures are within the range of from about 100.degree. C. to 
about 500.degree. C. On the basis of the results of the runs carried out 
it is believed that reaction temperatures within the range of from about 
200.degree. C. to about 350.degree. C. can be employed. 
The reaction pressures suited to the practice of this invention also vary 
widely. Reaction pressures within a range of from about atmospheric 
pressure to about 100,000 psig can be employed. On the basis of the 
results of the runs carried out it is believed that reaction pressures 
within the range of from about 500 psig to about 4000 psig can also be 
employed. 
If desired, the processes of this invention can be carried out in the 
presence of a polymerization inhibitor. The use of the inhibitor often 
advantageously limits said reactions such as the dimerization or 
polymerization of the olefinically unsaturated mononitrile. When a 
polymerization inhibitor is employed, it is generally desirable that an 
amount within the range of from about 0.001 to about 5 percent by weight 
polymerization inhibitor based on the weight of unsaturated mononitrile 
reactant be employed; however, amounts ranging from about 0.1 to about 1 
can also be employed based upon the runs carried out. A few examples of 
suitable inhibitors include hydroquinone,2,6-di-tert-butyl-para-cresol, 
2,6-di-tert-butylhydroquinone, 4-tert-butylcatechol, 
para-hydroxydiphenylamine, and the like, and combinations of any two or 
more thereof. 
The reaction of the above-described olefinic hydrocarbon reactant, 
olefinically unsaturated mononitrile reactant and monoadduct reaction 
product reactant can be carried out in the presence of an aqueous diluent. 
Generally the aqueous diluent comprising at least 50 weight percent water, 
and more often at least 80 weight percent water. The reaction can be 
carried out employing an aqueous diluent consisting essentially of water 
if desired. A co-diluent can be employed if desired and can be any solvent 
or diluent which is nonreactive with either the reactants or the reaction 
products. Examples of suitable co-diluents include benzene, toluene, 
para-xylene, ortho-xylene, meta-xylene, ethylbenzene, diethyl ether, ethyl 
propyl ether, dibutyl ether, tetrahydrofuran, dioxane, cyclohexane, carbon 
tetrachloride, methylene chloride, and mixtures of any two or more 
thereof. 
The diluent can be employed in any suitable amount. In general the diluent 
will be employed in an amount in the range of about 0.01 to about 40 parts 
by weight of total diluent per part by weight of olefinically unsaturated 
mononitrile reactant charged to the reaction zone. Based upon the results 
obtained employing 0.5 parts by weight of total diluent per part by weight 
olefinically unsaturated mononitrile reactant, the amount of diluent 
currently preferred is in the range of about 0.1 to about 20 parts by 
weight of total diluent per part by weight of olefinically unsaturated 
mononitrile reactant charged to the reaction zone. The advantages of the 
aqueous diluent system include improved selectivity to the desired 
olefinically unsaturated nitrile and reduced amounts of heavy polymeric 
byproduct. This latter byproduct is particularly objectionable because it 
tends to foul reactor surfaces. 
A convenient method of carrying out this invention to produce a dinitrile 
comprises heating a mixture of an olefinically unsaturated mononitrile 
(e.g. acrylonitrile), an olefinic hydrocarbon compound (e.g. isobutylene), 
and a monoadduct reaction product reactant (e.g. a mixture of 
5-methyl-5-hexenenitrile and 2,4-dimethyl-4-pentenenitrile) in a reaction 
pressure vessel at a temperature within the range of about 240.degree. to 
about 350.degree. C. and at pressures in the range of about 500 to about 
4000 psig, the mol ratio of the olefinically unsaturated mononitrile to 
the olefinic hydrocarbon being in the range of about 5:1 to about 0.2:1, 
and the concentration of the monoadduct reaction product reactant in the 
reaction mixture being in the range of about 20 to about 80 weight 
percent. Thereafter, the resulting olefinically unsaturated dinitrile 
reaction product is readily isolated from the reaction effluent mixture by 
any convenient product recovery method, such as fractional distillation. 
The reaction can be carried out until the mononitrile reactant and/or the 
olefinic hydrocarbon reactant is depleted from the reaction media in 
apparatus well known to the art and suited to either batch or continuous 
reaction conditions. 
If desired, the reaction can be carried out in the presence of any suitable 
promoter, for example an organo derivative of a Group VA element defined 
by the following formula 
EQU R.sup.V.sub.m ZH.sub.3-m 
wherein each R.sup.V is independently selected from the group consisting of 
aryl, alkaryl, cycloalkylaryl, araryl, aryloxy, alkaryloxy, and 
arylaryloxy; wherein each R.sup.V group contains from 6 to 12 carbon 
atoms; Z is selected from the group consisting of N,P,P.dbd.O. As, Sb, or 
Bi; and m is 2 or 3. Illustrative of organo derivatives of the Group VA 
elements defined by the above formula are the following compounds: 
triphenylphosphine, diphenylphosphine, tris(hexylphenyl)phosphine, 
tris(cyclohexylphenyl)phosphine, dinaphthylphospine, 
tris(4-biphenyl)phosphine, tris(4-butylphenyl)phosphine, triphenylamine, 
diphenylamine, tris(3,5-dipropylphenyl)amine, triphenylarsine, 
tris(pentylphenyl)arsine, triphenylbismuthine, diphenylarsine, 
diphenyl-4-biphenylphosphine, tris(p-tolyl)stibine, 
tris(3,5-dimethylphenyl)bismuthine, diphenyl(4-ethylphenyl)phosphine, 
diphenoxy(phenyl)phosphine, diphenyl(p-methylphenoxy)-phosphine, 
triphenylphosphite, diphenyl(p-tolyl)phosphine, triphenylphosphate, and 
mixtures of any two or more thereof. The variant designated by n in 
mixtures of promoters represented by the formula R.sup.V.sub.m ZH.sub.3-m 
can vary, with the arithmetical sum of the value of m of individual 
promoters, from 2 to 3. The term "reaction promoting material" includes 
materials commonly called catalysts as well as materials commonly called 
promoters. 
If employed, the amount of promoter utilized in the process of this 
invention can be selected over a wide range. In general, the mol ratio of 
promoter to unsaturated mononitrile reactant charged to the reaction zone 
is in the range of about 1:20 to about 1:1, although more often the mol 
ratio of promoter to unsaturated mononitrile reactant charge is in the 
range of about 1:10 to about 1:3. 
The following examples are presented in further illustration of the 
invention but are not to be construed so as to unduly limit the invention.

EXAMPLE I 
The three runs of this example are control runs for the instant invention. 
These runs were carried out by charging a 1 liter autoclave equipped with 
heating and stirring means with 70 grams of acrylonitrile, 315 grams of 
the monoadduct reaction product of acrylonitrile and isobutylene which had 
been previously prepared and recovered. In the first run no additives were 
added; in the second ammonia, a known isomerization inhibitor additive 
(not an isomerization inhibitor within the scope of the present invention) 
was introduced; and in the final run, 35 grams of water was added. The 
reactor was then flushed with nitrogen, charged with 160 grams of 
isobutylene and heated at 270.degree. C. for 2.5 hours. The pressure 
employed was autogeneous and was about 2000 psig. The resulting reaction 
mixture was processed by fractional distillation and the recovered 
monoadduct analyzed by gas-liquid phase chromatography. A comparison of 
the gas-liquid phase chromatography (GLC) peak area percent for the 
undesired isomer (5-methyl-4-hexenenitrile) in the starting material 
(monoadduct) with the same GLC peak area percent in the recovered 
monoadduct provides a measure of the extent of isomerization of monoadduct 
that took place during the reaction period. The gas-liquid phase 
chromatography analyses were, of course, conducted under the same 
conditions in each instance. The results of these three runs are presented 
below in Table I. 
Table I 
______________________________________ 
Run H.sub.2 O 
Additive GLC Peak Area % 
No. Wt. % Type Wt. % Starting MA 
Product MA 
______________________________________ 
1 0 none -- 0.16 0.35 
2 0 ammonia 1.6 0.16 0.28 
3 50 none -- 0.16 0.90 
______________________________________ 
.sup.a Based on weight of monoadduct charged (315 g.). 
.sup.b GLC peak area percent determined for 5methyl-4-hexenenitrile in 
monoadduct (MA). 
.sup.c MA represents monoadduct. 
Comparison of the results obtained in runs 1 and 3 demonstrate that 
although some isomerization to the undesired isomer occurs in the absence 
of water and isomerization inhibitor additive, the presence of water in 
the reaction mixture significantly promotes the formation of the undesired 
isomer in the absence of an isomerization inhibitor additive. Furthermore, 
in the absence of water, ammonia as an isomerization inhibitor additive, 
as shown in run 2, was only slightly effective under the conditions 
utilized in inhibiting the isomerization during the reaction period. 
EXAMPLE II 
A number of other runs were conducted in the same apparatus as previously 
described in Example I. The same amounts of acrylonitrile, monoadduct and 
isobutylene and the same techniques for measuring the extent of monoadduct 
isomerization during the reaction period were employed as in Example I. 
All of the runs in this example employed water as part of the reaction 
mixture in the amount of 50% by weight based on the weight of 
acrylonitrile charged to the reaction mixture. A variety of compounds were 
examined for their isomerization inhibitory effect under the conditions 
described. Included in this series of runs are several runs which are 
carried out according to the instant invention. Results of these runs are 
presented in Table II below. Run 3 of Example I, a control run, is also 
included in this tabulation for convenience in comparison with the results 
obtained in the other runs of the instant example. Run 6 of the instant 
example employed an isomerization inhibitor described in U.S. Pat. No. 
4,001,294; however, the amount employed was somewhat less than the amount 
recommended in the patent. 
TABLE II 
______________________________________ 
GLC Peak Area %.sup.b 
Run Additive Starting Product 
No. Type Wt. %.sup.a 
MA MA 
______________________________________ 
3 none -- 0.16 0.90 
4 Lithium acetate 0.06 0.16 0.53 
5 Ammonia 1.6 0.16 0.58 
6 EDTA.sup.c 0.002 0.16 0.85 
7 Sodium methoxide 0.11 0.16 0.58 
8 Lithium hydroxide 
0.22 0.16 0.53 
9 Sodium acetate 0.31 0.16 0.42 
10 Potassium monohydrogen 
orthophosphate 0.31 0.16 0.37 
11 Sodium carbonate 0.22 0.16 0.43 
12 Potassium oxalate 
0.31 0.16 0.13 
13 Potassium hydrogen 
terephthalate 0.31 0.16 0.28 
14 Potassium oxalate 
0.11 0.16 0.14 
15 Sodium citrate (tri-salt) 
0.22 0.16 0.23 
______________________________________ 
.sup.a Based on weight of monoadduct charged (315 g). 
.sup.b GLC peak area percent determined for 5methyl-4-hexenenitrile in 
monoadduct (MA). 
.sup.c Trisodium salt of ethylenedinitrilo)tetraacetic acid. 
Of all the runs presented in Table II, only those runs which employed 
potassium oxalate showed essentially complete inhibition of isomerization 
to the undesired isomer. All of the runs were better than the control run, 
run 3, which employed no additive, in the sense that the amount of 
isomerized monoadduct was less but, in each instance, the amount of 
undesirable monoadduct isomer in the recovered monoadduct was higher than 
in the starting monoadduct material. Runs 12 through 15 demonstrate the 
inhibiting effect of inhibitors of the present invention under the 
conditions employed. While the results of run 13 do not appear to be 
better than control run 2 in which ammonia was employed as the 
isomerization inhibitor, run 13 was carried out employing water in the 
reaction mixture and run 2 was carried out in the absence of water, a 
compound that clearly promotes isomerization to the undesired isomer as 
evidenced by run 3 described above. Runs 12 and 14 employing potassium 
oxalate provided the best results under the conditions employed. 
EXAMPLE III 
Another series of runs was carried out in essentially the same manner as 
that previously described in Examples I and II above and utilizing the 
same techniques for measuring the extent of monoadduct isomerization. In 
each run of the instant example, the diluent employed was water and the 
amount of water charged to the reaction mixture was 25 weight percent 
based on the amount of acrylonitrile charged. The runs of this example 
employed either potassium oxalate according to the instant invention or 
the trisodium salt of (ethylenedinitrilo)tetraacetic acid (EDTA). The 
latter compound is an isomerization inhibitor within the scope of those 
disclosed in U.S. Pat. No. 4,001,294. The results of these runs are 
presented in Table III below. 
Table III 
______________________________________ 
Run Additive GLC Peak Area %.sup.b 
No. Type Wt. %.sup.a 
Starting MA 
Product MA 
______________________________________ 
16 EDTA.sup.c 0.002 0.16 0.37 
17 EDTA 0.02 0.16 0.16 
18 EDTA 0.01 0.16 0.20 
19 EDTA 0.002 0.16 0.33 
20 EDTA 0.006 0.16 0.23 
21 Potassium oxalate 
0.11 0.16 0.10 
22 Potassium oxalate 
0.006 0.16 0.10 
23 Potassium oxalate 
0.01 0.16 0.10 
24 Potassium oxalate 
0.0002 0.16 0.10 
______________________________________ 
.sup.a Based on weight of monoadduct charged (315 g). 
.sup.b GLC peak area percent determined for 5methyl-4-hexenenitrile in 
monoadduct (MA). 
.sup.c Trisodium salt pf (ethylenedinitrilo)tetraacetic acid. 
The results of Table III demonstrate again the high effectiveness of 
potassium oxalate as an isomerization inhibitor for the monoadduct. 
Furthermore, potassium oxalate is shown to be effective as an 
isomerization inhibitor at extremely low levels. Run 17 which utilized the 
prior art isomerization inhibitor additive, when compared with run 24 
indicates that about 100 times as much of the prior art additive is 
required to achieve essentially no isomerization in the monoadduct.