Method for controlling the reactivity of an ozonization reaction product

A method for controlling the reactivity of an ozonized reaction mixture formed by ozonizing an unsaturated compound, wherein the reactivity of the ozonized reaction mixture is controlled by introducing a reactivity controlling amount of a saturated fatty acid into the reaction mixture before contact with the ozone.

BACKGROUND OF THE INVENTION 
It is known that carboxylic acids can be prepared by ozonization of 
unsaturated compounds followed by reaction of the ozonized material with 
oxygen at an elevated temperature, optionally in the presence of a 
catalyst to form the carboxyl group. 
RELATED ART 
The processes are particularly useful for forming dicarboxylic acids from 
unsaturated carboxylic acids and unsaturated carboxylic acid esters. The 
details of such processes are set out in U.S. Pat. No. 2,813,113 to Goebel 
et al. and U.S. Pat. No. 5,292,941 to Kigawa et al., the contents of which 
are incorporated herein by reference. Japanese Patent Application No. 
4-124311, filed Apr. 17, 1992, published as Japanese Patent Publication 
5-294957 on Nov. 9, 1993, discloses a process for producing an ozonization 
product with reduced reactivity by ozonization of an unsaturated 
carboxylic acid ester with limited amounts of carboxylic acids present. 
Ozonization of ethylenically unsaturated compounds can be conducted in the 
presence of a diluent to provide a reaction mixture with a low viscosity. 
For ease of operation, ozonization of unsaturated carboxylic acids or 
esters of unsaturated carboxylic acids is generally carried out in the 
presence of a saturated carboxylic acid or an ester of a saturated 
carboxylic acid as a diluent. Preferably, the saturated carboxylic acid or 
ester thereof is a product of the process. 
The ozonization reaction product is a complex mixture which is dependent 
upon the unsaturated starting material and the diluents, if any, which are 
present in the mixture which is ozonized. The articles THE PEROXIDE 
SPECIES GENERATED BY OZONOLYSIS OF OLEIC ACID OR METHYL OLEATE IN A 
CARBOXYLIC ACID MEDIUM, Louis Reprovic, JAOCS, vol. 69, No. 2 (February 
1992) and STRUCTURES OF OZONOLYSIS PRODUCTS OF METHYL OLEATE OBTAINED IN A 
CARBOXYLIC ACID MEDIUM, Naoki Nishikawa, et al., JAOCS, vol. 72, No. 6 
(1995) disclose the ozonization products which appear in the largest 
quantities in the ozonization reaction mixture. The articles disclose that 
the ozonization reaction mixture generally contains the following 
compounds in various proportions: 
##STR1## 
In the structures (I), (II), and (III) the groups R, R' and R" represent 
groups present in the unsaturated compound or saturated carboxylic acid 
diluent present in the reaction mixture which is to be ozonized. 
The ozonized compounds have different rates of reaction and decomposition. 
Compound (I) reacts much slower than compounds (II) and (III). It would be 
useful, if the composition of the ozonization reaction mixture could be 
controlled, to either reduce the time the mixture must be contacted with 
oxygen to form carboxyl groups or provide a less reactive and more stable 
mixture. 
SUMMARY OF THE INVENTION 
According to the present invention, the reactivity of the ozonization 
reaction mixture can be controlled by using a saturated carboxylic acid 
diluent in a reactivity controlling amount, the carboxylic acid diluent 
having a chain length selected to provide an ozonization reaction mixture 
with a required reactivity. 
The invention comprises a method for controlling the reactivity of an 
ozonization reaction mixture formed by ozonization of ethylenically 
unsaturated compounds and particularly an unsaturated fatty acid, an ester 
of an unsaturated fatty acid or mixtures thereof, which comprises: 
contacting a mixture of the ethylenically unsaturated compound, the 
unsaturated fatty acid, the unsaturated fatty acid ester or mixtures 
thereof to be ozonized and a reaction mixture reactivity controlling 
amount of a saturated fatty acid or a mixture of saturated fatty acids 
having a chain length selected to provide an ozonized mixture with 
required reactivity, with ozone at a temperature of from about -40.degree. 
C. to about 50.degree. C. Applicants have discovered that reducing the 
chain length of the saturated fatty acid diluent increases the reactivity 
of the ozonated reaction mixture. The reactivity of the mixture can be 
controlled by adjusting the chain length of the saturated carboxylic acid 
diluent or mixtures of saturated carboxylic acids to obtain a reaction 
mixture with the required reactivity.

DETAILED DESCRIPTION OF THE INVENTION 
The term "reactivity" as used herein means the rate at which the ozonated 
reaction products decompose and react to form a carboxyl group. The 
reactivity of the ozonated reaction mixture is controlled by adjusting the 
amount and chain length of a saturated carboxylic acid used as a diluent 
in the reaction mixture. It is known that the reactivity of compounds (II) 
and (III) is much higher than the reactivity of compound (I). Applicants 
have discovered that the sum of the amount of compounds (II) and (III) in 
the ozonized reaction mixture increases as the chain length of a saturated 
fatty acid diluent is decreased. That is, the total of the amount of 
compounds (II) and (III) can be increased or decreased by adjusting the 
amount and chain length of the saturated fatty acid diluent present in the 
reaction mixture. Using equal weights or volumes of saturated fatty acid 
diluent, the shorter chain length acids provide more reactive reaction 
products. 
The ozonization process is generally carried out by contacting a mixture 
comprising an unsaturated fatty acid, unsaturated fatty acid ester or 
other ethylenically unsaturated compound or mixtures thereof and a diluent 
with a gas stream which comprises oxygen and ozone under conditions 
wherein the reaction temperature is maintained from about -40.degree. C. 
and about 50.degree. C. and preferably from about 10.degree. C. to about 
45.degree. C. Lower reaction temperatures provide ozonated reaction 
mixtures with lower amounts of unwanted reaction products. The temperature 
at which the ozonization is carried out is generally a compromise between 
the ability to provide low temperature cooling and the amount of unwanted 
reaction products in the ozonated reaction mixture. At a temperature above 
about 50.degree. C., the process is difficult to control and major amounts 
of unwanted reaction products are formed. At lower temperatures, it is 
difficult to provide a reaction mixture with a viscosity sufficiently low 
that it can be efficiently contacted with the gas mixture comprising ozone 
and oxygen. 
A saturated fatty acid diluent not only controls the reactivity of the 
ozonized reaction product but also controls the viscosity of the reaction 
mixture. It is known that the viscosity of an ozonized unsaturated fatty 
acid or ozonized unsaturated fatty acid ester increases as the amount of 
unsaturated fatty acid or unsaturated fatty acid ester which has reacted 
with ozone increases. The saturated fatty acid or saturated fatty acid 
ester diluent can reduce the viscosity to levels which make operation at 
temperatures below 10.degree. C. feasible. 
The gas comprising ozone and oxygen can contain nonreactive diluent gases. 
The use of diluent gases provides for a more easily controlled ozonization 
reaction. Inert gases such as carbon dioxide, or the noble gases such as 
argon, neon and the like, can be utilized to dilute the ozone-containing 
oxygen. Generally the ozone containing gas contains from about 0.5 to 
about 7% by volume ozone, the remainder being oxygen and inert diluent 
gas. Nitrogen is not a preferred diluent gas since at high concentrations 
it can form nitrogen-containing compounds in the reaction mixture. 
However, small amounts of nitrogen diluent in the gas mixture comprising 
ozone and oxygen can be tolerated. 
The unsaturated compound and the saturated fatty acid diluent can be 
contacted with the ozone-containing gas stream from sub-atmospheric to 
super-atmospheric pressure. However, due to the cost of fabricating the 
reaction vessels, pressures in the range of from about atmospheric to 
about 50 pounds per square inch gauge are preferred. 
The ozonization reaction mixture containing the ozonized unsaturated fatty 
acid or ozonized unsaturated fatty acid ester or mixtures thereof is 
contacted with oxygen essentially free of ozone to form two carboxyl 
groups at the position of the unsaturation which had been ozonized. The 
ozonized unsaturated fatty acid is generally contacted with the 
oxygen-containing gas stream substantially free from ozone at a 
temperature of from about 60.degree. C. to about 150.degree. C. and 
preferably between about 80.degree. C. and about 130.degree. C. and most 
preferably between about 100.degree. C. and about 125.degree. C. to react 
with the compounds (I), (II), and (III) to form the carboxyl groups. 
Complete decomposition of the ozonide, formed from the unsaturated fatty 
acid or unsaturated fatty acid ester, and formation of two carboxyl groups 
by contact with oxygen requires a substantial amount of time. Generally, 
the prior art teaches that a reaction time in a range of about three to 
about eight hours is required to substantially react and decompose the 
ozonide present in the ozonized reaction mixture. 
The decomposition of the ozonization product by contact with oxygen at an 
elevated temperature is generally carried out in a series of reaction 
zones. The ozonization product is introduced into a temperature-controlled 
reaction zone and mixed with a body of partially reacted ozonization 
product. Oxygen, preferably in the form of fine bubbles, is passed through 
the liquid in the reaction zone to react and decompose the ozonization 
reaction product. The temperature in the first reactor is generally 
controlled by a cooling means which removes the heat generated by the 
reaction. 
The partially reacted reaction mixture passes from the first reaction zone 
to a second reaction zone where additional oxygen, preferably in the form 
of fine bubbles, is passed through the reaction mixture. The second 
reaction zone, depending on the amount of reaction which has occurred in 
the first reaction zone, may require temperature control by cooling or 
require heating since the partially reacted ozonization product can 
contain only small amounts of material to be reacted. The number of 
reaction zones utilized in a particular process is dependent on the 
reaction time required and the ability to properly control the reaction 
temperatures. Generally three or more reaction zones are used. 
After the ozonization product has been reacted with oxygen at an elevated 
temperature to form the carboxyl groups, the carboxylic acids are 
generally separated and the saturated carboxylic acids are recycled in the 
required chain length range to control the reactivity of the ozonization 
product. 
The present invention has been discussed in relation to ozonization and 
decomposition of unsaturated fatty acids or fatty acid esters. However, 
the present invention can be utilized to control the reactivity of 
ozonization reaction mixtures formed by ozonization of ethylenically 
unsaturated bonds other than those contained in unsaturated carboxylic 
acids or esters of unsaturated carboxylic acids. 
The process of the present invention finds particular usefulness in the 
production of dicarboxylic acids by ozonization of unsaturated carboxylic 
acids or esters of unsaturated carboxylic acids. In particular, the 
process is particularly useful in preparing azeleic acid by ozonization of 
a mixture comprising oleic acid and the reactivity controlling saturated 
carboxylic acids. 
In the process of the invention, the reactivity controlling saturated 
carboxylic acids can be present in the reaction mixture in a weight ratio 
of ethylenically unsaturated compound, unsaturated carboxylic acid or 
unsaturated carboxylic acid ester or mixtures thereof to saturated 
carboxylic acid by weight of from about 5:1 to 1:5. Preferably, the ratio 
by weight of the ethylenically unsaturated compound, unsaturated 
carboxylic acid or unsaturated carboxylic acid ester to the saturated 
carboxylic acid is in the range of from about 4:1 to 1:4 and preferably in 
the range of from about 2:1 to 1:2. 
In addition to the amount of the saturated fatty acid diluent, the amount 
of the more reactive species (II) and (III) is affected by the chain 
length of the saturated fatty acid diluent. As the chain length of the 
saturated fatty acid diluent decreases, the sum of the amounts of the (II) 
and (III) compounds (the more reactive and more easily decomposed 
compounds) in the ozonated reaction mixture increases. When equal weights 
or volumes of the saturated carboxylic acid diluents are present in the 
mixture to be reacted with ozone, the mixture containing the shortest 
average chain length saturated carboxylic acid diluent produces the most 
reactive mixture after ozonization. 
As the reactivity of the reaction mixture is increased, by an increase in 
the amount of the more reactive species, the contact time at the elevated 
temperature between the ozonized reaction mixture and the 
oxygen-containing gas can be reduced. The reduction in the reaction time 
can substantially increase the plant capacity or decrease the size of the 
reaction vessels required for the oxidation-decomposition of the ozonized 
reaction product. The increase in the reactivity can be clearly seen from 
the following examples. 
The effect of the chain length of the saturated carboxylic acid was 
determined as follows: a mixture of 5 grams (17.7 mmol) of oleic acid and 
10.0 ml of carboxylic acid solvent (diluent) were added to a modified test 
tube (a 2.2 cm in diameter, 13 cm long test tube with a two-headed 50 ml 
round bottom flask fused to the top, a Claisen head with a sparge tube and 
reflux condenser was mounted on the top of the modified test tube 
reactor). The reactor containing the reagents was immersed in a 25.degree. 
C. water bath and an ozone/oxygen gas mixture was bubbled through the 
reaction mixture at 0.3 mmol O.sub.3 /minute until the reaction was 
complete. When the reaction was complete, a sample was taken for HNMR 
(CDCl.sub.3 : 10% solution) analysis. The peaks in the NMR analysis of the 
reaction mixture were analyzed and the compounds assigned according to 
known procedure. The results of the experiments are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Total 
1-Acyloxyalkyl- 
Acyloxy- 
Chain Length 
cis/trans 
1-Acyloxyalkyl- 
1-Hydroxy alkyl 
peroxy 
of Solvent 
1,2,4-Trioxolane(+) 
1-Hydro-peroxide 
peroxide (Erythro + 
(II) + (III) 
CH.sub.3 -(CH.sub.2).sub.x -CO.sub.2 H 
(I) (II) Threo) (III) 
Weight 
Example 
X Percent by Weight 
Weight percent 
Weight percent 
Percent 
__________________________________________________________________________ 
1 0 3.05 52.2 32.7 84.9 
2 1 7.14 56.4 26.8 83.2 
3 2 8.74 34.0 38.2 72.2 
4 4 10.39 28.3 40.4 68.7 
5 6 11.76 21.4 38.2 59.6 
6 7 12.06 20.4 37.3 57.7 
REBROVIC 
__________________________________________________________________________ 
Examples 1-6 clearly show that as the chain length of the saturated 
carboxylic acid diluent decreases, the amounts of the more reactive 
acyloxyperoxide compounds (II) and (III) in the reaction mixture increase 
and the amount of the less reactive compound (I) decreases. 
Examples 7 through 11 were carried out in a manner similar to Examples 1 
through 6, except that in Examples 8, 9 and 10, a mixture of acetic acid 
and pelargonic acid were utilized as the diluent. The ratio by volume of 
acetic and pelargonic acid and the amount of reactive species formed 
during the reaction as determined by HNMR analysis as in examples 1-6 are 
shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
cis/trans 
VOLUME TOTAL ACYLOXYPEROXY 
1,2,4-TRIOXOLANE 
ACETIC/ 
(II) + (III) (I) 
EXAMPLE 
PELARGONIC 
percent by weight 
percent by weight 
__________________________________________________________________________ 
7 0/100 57.7 12.06 
8 25/75 73.0 5.81 
9 50/50 74.8 4.16 
10 75/25 79.3 3.94 
11 100/0 84.9 3.05 
__________________________________________________________________________ 
Table 2 clearly shows that as the ratio of acetic to pelargonic acid is 
increased, the total amount of the acyloxyperoxy-type compounds (II) and 
(III) in the reaction mixture increases and the amount of cis/trans 
1,2,4-trioxolane (I) decreases. The acyloxyperoxy compounds are 
substantially more reactive than the 1,2,4-trioxolane compounds. The 
average chain length of the saturated acid diluent affects the reactivity 
of the reaction mixture. Mixtures of acids of different chain lengths can 
be used to provide a reaction mixture with a required reactivity. 
Examples 12 and 13 were carried out to determine the reactivity of the 
ozonide compounds in the ozonized reaction mixture. In examples 12 and 13, 
a mixture of 35.0 g of oleic acid and 35.0 g of octanoic acid were added 
to a modified test tube (2.2 cm diameter, 21.5 cm long test tube with a 
four head 100 ml round bottom flask fused to the top). The reactor was 
fitted with a sparge tube and a reflux condenser. The reactor containing 
the reagents was immersed in a 25.degree. C. water bath and an 
ozone/oxygen gas mixture was bubbled through the reaction mixture at 1.0 
mmol O.sub.3 /min until the reaction was complete. 
A portion of the reaction mixture was placed in a reactor as described in 
Example 1, and the reactor containing the reaction mixture was immersed 
immediately in a water bath at 83.degree. C. and oxygen gas or nitrogen 
gas was passed through the mixture. Samples were taken for analysis by 
HNMR (CDCl.sub.3 : 10% solution) and the peroxide content was determined 
by an iodometric peroxide method. The results of the experiment are shown 
in FIG. 1, FIG. 2, FIG. 3 and FIG. 4. 
FIG. 1 is a plot of the concentration of the major ozonide components in 
the ozonated reaction mixture against time over which N.sub.2 was bubbled 
through the mixture at 83.degree. C. The acyloxyperoxide compounds (II) 
and (III) react rapidly and are reduced to low concentrations in a short 
time. The trioxolane component (I) reacts slowly and its concentration is 
only slightly reduced after 3 hours. 
FIG. 2 is a plot of the amount of products formed by decomposition of the 
ozonide and ozonide which remains unreacted in the mixture in the 
experiment of FIG. 1. Without the presence of oxygen, aldehyde (which 
co-forms with carboxylic acid) formed by decomposition of the oleic acid 
ozonide can not react to form a carboxyl group. Carboxylic acid and 
aldehyde are theoretically formed on a mole for mole basis when the 
ozonide of oleic acid decomposes. When oxygen is present, the aldehyde 
group reacts to form a carboxyl group. In the plot of the results of the 
experiment shown in FIGS. 1 and 2, as the oleic acid ozonide decomposes 
the amount of azeleic acid, pelargonic acid (NOT SHOWN) and aldehyde 
increases. As can be seen, the amount of component (I) decreases slowly 
while components (II) and (III) disappear from the mixture relatively 
quickly. 
FIG. 3 is a plot of the composition of the ozonated reaction mixture of 
equal volumes of oleic acid and octanoic acid held at 83.degree. C. with 
oxygen passing through the mixtures against time. The components (II) and 
(III) in the mixture decompose rapidly while the component (I) in the 
mixture decomposes slowly. After two hours component (II) has 
substantially disappeared from the mixture. 
FIG. 4 is a plot of the same experiment as shown in FIG. 3, showing the 
amount of ozonide, azeleic acid and aldehyde in the mixture as a function 
of time. The concentration of ozonide is rapidly reduced initially. After 
the components (II) and (III) have been substantially reacted from the 
mixture, the ozonide is decomposed more slowly as compound (I) reacts. 
Since oxygen is present, the amount of aldehyde in the mixture remains at 
a low level when compared to FIG. 2. The amount of azeleic acid reaches a 
substantially higher concentration when compared to FIG. 2. 
At higher temperatures, the decomposition reaction is more rapid. As the 
concentration of ozonide and aldehyde in the mixture is reduced, it can be 
advantageous to introduce a catalyst into the mixture to increase the rate 
of the decomposition reaction and oxidation of the aldehyde. 
FIGS. 1-4 show that compounds of the type (II) and (III) are substantially 
more reactive than compounds of the type (I). 
The results of the experiments show that the acyloxyperoxy compounds (II) 
and (III) are substantially more reactive than the 1,2,4-trioxolane 
compound (I). FIGS. 1-4 clearly show that the acyloxy compounds are 
substantially more reactive than the 1,2,4-trioxolane compounds. Since the 
acyloxy compounds are substantially more reactive than the trioxolane 
compounds, and the amount of the acyloxy compounds can be controlled by 
controlling the amount and type of the carboxylic acid diluent, the method 
of the present invention can be used to control the reactivity of the 
ozonized reaction mixture. 
If the ozonization process provides an ozonized product which is too 
reactive to be safely handled in a subsequent oxidation process, the 
reactivity can be reduced by selecting the amount and type of solvent to 
provide an ozonized reaction mixture with a lower reactivity. 
Theoretically, the lowest reactivity can be achieved by not using a 
carboxylic diluent; however, other diluents must be used to provide a 
reaction mixture which can be effectively contacted with the ozone/oxygen 
mixture. Use of non-carboxylic acid diluents makes the process more 
complex and requires additional purification steps. The present invention 
provides a method for controlling the reactivity of the ozonized reaction 
mixture using carboxylic acids which are related to or products of the 
process. 
The present invention has been described in relation to ozonization of 
oleic acid, however, the invention can be applied to ozonization of any 
ethylenically unsaturated compound in which the double bonds are reacted 
with ozone in the presence of a diluent material. The amount of the 
saturated carboxylic acid and the chain length of the saturated carboxylic 
acid can be utilized to provide an ozonized reaction mixture with a 
required reactivity. The method of the present invention can also be 
utilized to lower the reactivity of an ozonization process by utilizing a 
carboxylic acid diluent having a longer chain length. Saturated carboxylic 
acids with chain lengths from 2 to about 22 carbon atoms can be utilized 
as diluents for the process.