I
D. R. LEVERING and A. L. GLASEBROOK Hercules Powder Co., Wilmington, Del.
Oxonation of Rosin Rosin reacts with carbon monoxide and hydrogen to add methylol group to the unsaturated components. A solvent and preformed cobalt carbonyl are needed for high yields. These new derivatives of rosin (oxonated rosin, polyesters, and other esters from oxonated rosin) have properties which should lead to commercial exploitation
THE
oxo or hydroformylation reaction, discovered by Roelen (7), has been widely exploited since World War 11. In simplest terms the reaction involves addition of carbon monoxide and hydro-
gen to a n olefin to give an aldehyde (Equation 1). Under many conditions the oxo reaction is followed by a second step in which the aldehyde is hydrogenated to an alcohol (Equation 2).
Oxo Reaction 0
0
RCH-cHz
-k
co
3000 p s i . or higher + HZ cobalt catalyst
/-
RCHzCH2C-H
or RCH-C-H
0
// + HZ or nickel cobalt RCH2CHzC-H catalyst
//
’RCHzCHtCHzOH
(1 )
The catalysts are dicobalt octacarbonyl, [Co(CO)4]2, and cobalt hydrocarbonyl, HCo(CO)r, which are easily formed in situ from cobalt salts such as cobalt acetate, oleate, or naphthenate. I n general, the yields are high (90% or better), which is one of the reasons for the considerable industrial importance of the reaction. The commercial significance of the oxo reaction has been reviewed by Sherwood ( 8 )and the mechanism and kinetics have been discussed by Wender and Sternberg ( 7 7). Although with simple unbranched monoolefins the reaction is straightforward, reactions of conjugated olefins, dienes, hindered olefins, and substituted
Proposed components of oxonated rosin VOL. 50, NO. 3
MARCH 195%
317
olefins are not necessarily predictable as to course and often occur with difficulty or not a t all. With butadiene, one double bond is oxonated, while the other is hydrogenated (70) (Equation 3). Low yields are obtained with amethylstyrene (4) (Equation 4) and higher olefins (4)such as polypropylene and polyisobutene (Equation 5). Oxonation of Butadiene and Hindered Olefins CHz-CH-CH=CH? CH3CH&H&HeCH0
+ CO + He 24y0yield
-L
(3)
CH 3
+ CO + He+
( C ~ H ~ ) XCO (iso-CdHs),
+ HZ
__f
Aldehydes
Of the unsaturation present in rosin, only the exocyclic double bond in pimaric type acids would be expected to be readily oxonated; the remaining unsaturation, consisting of hindered olefins (such as dihydroabietic acid) or conjugated dienes (abietic type) would be difficult to oxonate. Ronin contains about 14% pimaric-type acids (2). Under specific conditions, however, reaction between rosin, carbon monoxide, and hydrogen occurs, to give a product in which apparently a methylol group (-CH20H) is added to one double bond and hydrogen to the other. Under preferred conditions, rosin and preformed cobalt carbonyl are dissolved in a n inert solvent such as cyclohexane and heated a t 200" C. in a pressure vessel under a pressure of hydrogen-carbon monoxide mixture of 5000 p.s.i. for about 2 hours. (The value of preparing the cobalt carbonyl separately is discussed later.) This process adds 0.8 to 0.9 mole of methylol group per mole of rosin to give oxonated rosin.
+
alcohols < l o % yield ( 5 )
T h e main constituents of rosin are composed of two types of acids:
Reaction Variables Solvent. T h e most important single variable in this reaction is the use of solvent (Figure 1).
PlMARlC TYPE
ABIETIC TYPE
89.5 O/o YIELD
d
2000
m
x -50% SOLVENT
-I I
0
50
100
Figure 1.
31 8
150
200 250 300 TIME IN MINUTES
350
400
Effect of solvent on oxonation of rosin
INDUSTRIAL AND ENGINEERING CHEMISTRY
450
500
Figure 1 shows the amount of gas absorbed during reaction as a function of time. Under preferred conditions, when 50% by weight of solvent is used, a rapid reaction occurs which results in a high (89.5%) yield. Under the same conditions with 4% solvent, a similar reaction takes place, giving essentially the same yield of product. When no solvent is used (preformed catalyst). there is a long induction period before reaction occurs and the product contains significantly less methylol group. Finally, when cobalt acetate, a common catalyst precursor used by many workers in the field, is used without solvent, no reaction occurs after 6 hours a t 200" C. This striking effect of solvent on the yield was unexpected and has not been previously reported. The reason for this effect is not readily apparent. The free acid group on the rosin nucleus may be the cause of difficulty. There are few if any examples of free acids being oxonated under the usual conditions. The esters are more commonly used. The solvents used, of course, did not react with either the starting material or the product. Such solvents as aromatic or saturated hydrocarbons or ethers were used. Catalysts. The most active catalyst is cobalt carbonyl, prepared separately rather than during reaction. The greater activity of cobalt carbonyl over cobalt acetate is illustrated in Figure 1. The preformed catalyst gives a 67% yield; under the same conditions with cobalt acetate no reaction occurs. Under preferred conditions (50% solvent, 200 " C,), cobalt carbonyl gave a yield of 89.5%, whereas cobalt acetate gave a yield of 42%. With the preformed catalyst, reaction starts a t a lower temperature than Ivith cobalt acetate (120' us. 200" C.), which again shows the greater activity of cobalt carbonyl in this reaction. The catalyst was charged as a solution of cobalt carbonyl in a solvent and in the amount of 0.5 to 1% cobalt based on the rosin used. Temperature. With active catalysts rosin is oxonated at temperatures as low as 120" C. The upper limit of temperature is about 230" C., above which decomposition of the rosin starts to become appreciable. At 120" to 140" C. and 1 to 1 hydrogen-carbon monoxide ratio, it is possible to prepare the aldehyde derivative, but only in low yields. Figure 2 gives the moles of functional group formed as a function of temperature. Above 160' C., alcohol becomes the major product, and finally a t 200" C., all the aldehyde has been hydrogenated. T h e amount of acid (as ester) prepared increases with temperature. Hydrogen-Carbon Monoxide Ratio. The ratio of hydrogen to carbon monoxide is not critical. At low tempera-
OXONATION O F ROSIN tures using a 1 to 1 ratio it is possible to stop a t the aldehyde derivative. However, as the temperature is raised, the aldehyde is hydrogenated to the alcohol even with the 1 to 1 mixture, because the gas mixture is always present in excess. Under the preferred conditions for preparing oxonated rosin, 2 to 1 hydrogen-carbon monoxide ratio is used. Types of Compounds. Compounds which react readily under the conditions described are N-wood rosin, gum rosin, tall oil (crude or distilled), Belro rosin, K-wood rosin, Abalyn (methyl ester of rosin), rosin nitrile, and pure rosin acids. Rate of Reaction. ROSIN. T h e reaction between rosin in a solvent and carbon monoxide and hydrogen is exothermic. Reaction usually starts on the heat-up a t about 160' C. and the heat generated helps to carry the temperature to 200" C . I n batch experiments reaction is complete in about 2 hours. Quantitative work has not been done on determining the rate of reaction, but from the plot (Figure 1) of gas absorbed us. time, the rate seems to be zero order. COMPONENTS OF ROSIN. When the various components of rosin were oxonated separately, rosin neutrals and abietic and dextropimaric acids reacted faster than dihydroabietic acid; dehydroabietic acid did not react.
Chemistry of Reaction Because rosin is a mixture of several components which are not readily separated, only mass analyses are possible. Table I shows typical analyses for the N-wood rosin starting material and oxonated rosin. T h e acid number has decreased, while the amount of alcohol and melting point have increased. Table I1 gives the mole fractions of each functional group present in the original rosin and the oxonated product. The amounts of each group were calculated from the analyses given in Table I and apparent molecular weights of 336 for rosin and 366 for oxonated rosin.
X
0.90
0.80
0.70
n
$
a
t
c u
n
2o.
09
2 = 0.18
5.06
OXONATED ROSIN Apparent molecular wt.
I /
X
.-ALDEHYDE
0.30
iz:,
