Catalyst-Solvent Systems for Dimerization of Abietic Acid and Rosin Bernard A. Parkin, Jr., and Walter H. Schullerl Southern Marketing and Nutrition Research Division, Naval Stores Laboratory, ARS, U S D A , Olustee, FL 32072
The dimerization of abietic acid in chloroform solution with sulfuric acid catalyst was run in a fashion similar to that described by Sinclair et al. The results obtained were similar, but yields were generally 10% lower. Much lower yields of dimer were observed in benzene, isooctane, and heptane. Acetic acid solutions gave higher yields. Sulfuric acid catalyst ( 1 00%) was used in most of the work in acetic acid solution to obtain yields of approximately 75y0 dimer, but aqueous sulfuric acid gave yields up to 83%. The products from acetic acid also showed retention of about 90% of the original resin acid function.
T h e wide commercial use of dimerized rosin in adhesives, lacquers, varnishes, and inks and the lack of critical work published on its production have prompted investigation in this area. Work done by Sinclair et al. (1970) on pure abietic acid showed sharp maxima in the plots of dimer yield against milliliters of concentrated sulfuric acid used per 1.5 grams of abietic acid in chloroform solution. This would indicate a rather narrow range of efficient operating conditions in this system. The present investigation was undertaken to determine whether frequently used systems show similar behavior and to screen other catalyst-solvent systems. Abietic acid was chosen as the starting material here also. Experimental
The experiments on abietic acid were run by two methods. I n both, abietic acid solutions were made in the chosen solvent to a concentration of 1-1.5 grams in 20 ml. With solvents resulting in heterogeneous systems, aliquots (generally 20 ml) were placed in individual flasks, and the appropriate amounts of catalysts added to each. The mixtures were placed in a water bath a t 44OC, stirred during the course of the reactions with magnetic stirrers, then hydrolyzed with water, and washed to a pH of 6 with 5 1 0 % sodium sulfate solution. The 44OC reaction temperature and concentration of 1.5 grams abietic acid per 20 ml of chloroform used by Sinclair et al. (1970) were used here in chloroform and benzene and in some of the isooctane and heptane runs. The solubility of abietic acid in isooctane and heptane necessitated lowering the concentration to 1 g/20 ml to avoid precipitation; this procedure was adopted in the remainder of the work. With solvents resulting in homogeneous systems, larger volumes of the solution were treated with the appropriate amount of catalyst and mixed by swirling. As a matter of convenience, the homogeneous solvent runs were made a t room temperature (25'C) except in screening runs where T o whom correspondence should be addressed. 156 Ind. Eng. Chem. Prod.
Res. Develop., Vol. 1 1,
No. 2, 1972
mixtures were heated on the steam bath in attempts to force the reactions and as otherwise noted. I n all abietic acid runs where sulfuric acid was the catalyst, 100% acid was used. I n the acetic acid runs with lower percentage sulfuric acid catalysts, the calculated amount of water was added to the abietic acid solution; then an identical quantity of 100% sulfuric acid was added to each solution. The solutions were then sampled a t the times chosen, and the samples were hydrolyzed with water, diluted, and extracted with ether. The ether solutions were then washed t o a pH of 6, as before. I n all cases the final solutions of the products were dried over anhydrous sodium sulfate, filtered, and evaporated on a rotary evaporator under aspirator vacuum. The one exception to this procedure was with the 75% sulfuric acid catalyzed runs in which the acid was mixed beforehand, and the quantities indicated were added t o the solutions. Samples of the products were esterified with excess etherial diazomethane, and the esters were analyzed for dimer content, according to the gas-liquid chromatographic method of Sinclair et al. (1971), using a 4ft 3/le-in. 80,400 mesh 3% SE-52 on Gas Chrom Q column prepared and conditioned overnight a t 35OoC, open to the atmosphere, according to their directions. Neutral equivalents were determined as described by Parkin et al. (1969), and ball and shouldered ring softening points on the resins were run in glycerol (ASTM, 1958). Discussion
Runs made in chloroform using 100% sulfuric acid catalyst gave maxima a t catalyst concentrations close to 0.55 ml/l.5 g of abietic as found by Sinclair et al. (1970). Sinclair reported yields as high as 85%; those found here were generally around 75%. Acid retention and material balances were approximately the same as those previously reported. The yield of dimer in benzene plotted as a function of milliliters of 100% H2S04 per gram of abietic acid in 20 ml of benzene indicates a maximum between 0.25 and 0.30 ml of acid. The maximum value obtained was 61% a t 0.25 ml. When a concentration of 1.5 grams of abietic acid in benzene was used with 0.55 ml of
Table 1. Summary of Results of Dimerization of Abietic Acid with Various Catalyst-Solvent Systems
Solvent
CHCL Benzene Heptane Isooctane
Abietic acid concna
Catalyst
1.5 1
DMSO DMSO
1 1 1 1
Acetic acid Acetic acid Acetic acid Acetic acid Acetic acid Acetic acid Acetic acid Acetic acid ilcetic acid
1 1 1 1 1 1 1 1 1
Gram of abietic acid per 20 ml of solvent. a gas.
Catalyst concd
0.33 0.25 0.12 0.22 0.5-2.0 0.5-5.0 1.0 e c
0.4 c
1.0 1.1 1.3 1.6
Dimer yield,
Resin acid,
Recovery,
96
96
96
75 61 44 49 0 0.3 2 5 2 19 81 75 83.6 80.4 67.4
82 74 78 79 ...
98 100 99 98 ...
I
.
... ...
.
... ... ... ... 95 91 92 94 92
...
... ... 99 97 99 100 98
of catalyst per gram of abietic acid. Catalyst bubbled through the solution as
acid, yields of 57 and 58% were obtained. Sinclair reported 78% dimer on a run under these conditions. When heptane or isooctane was used as the solvent, the highest yields were 44 and 49y0, respectively, with catalyst concentrations of 0.2-0.3 ml/g of abietic acid. Figure 1 shows the d a t a obtained in benzene, isooctane, and heptane a t a concentration of 1 gram of abietic acid per 20 ml of solvent. All the systems studied to this point were heterogeneous. The following systems were homogeneous except where phase separation occurred with high concentrations of catalyst. Dimethylsulfoxide (D1ISO) as solvent failed to give appreciable dimer formation using either sulfuric acid or hydrogen fluoride as the catalyst. Acetic acid gave good results with sulfuric acid as the catalyst, and one of the better yields in the entire study to date was obtained using hydrogen fluoride in acetic acid. Phosphoric acid (85% commerical), hydrogen chloride, trifluoromethanesulfonic acid (TFLISA) loo%, and hydrogen bromide were also used as catalysts in acetic acid. Kone of these catalysts gave promising dimer yields. The best of these was 19% dimer after 42 h r a t 25OC. Results with these catalysts are summarized in Table I. Typical results with 100% sulfuric acid in acetic acid are shown in Table 11. These data show 1 ml 0 acid to be an effective catalyst for the polyof 1 0 0 ~ sulfuric merizatioii of 1 gram abietic acid in 20 ml of acetic acid even at short reaction times. This catalyst ratio was used in all other acetic acid experiments except as noted for the 75% sulfuric acid run. Whereas the phase separation in the heterogeneous mixtures facilitates removal of the bulk of the catalyst, it also results in the abietic acid or other reacting resin acids contacting t h e sulfuric acid or sulfuric acid complex in concentrated form. Homogeneous media allow for dilution of the acid and result in milder reaction conditions. The failure to form dimer j i i DMSO may have been due to the reported basic iialure of DMSO (Oae et al., 1961). Acetic acid provides a niedia in which the full acid strengths of the catalysts cculd be effective and has proven t o be a good solvent for the dimerization reaction. The effect of the presence of water was studied by adding quant8itiesof water sufficient
Table II. Dimerization of Abietic Acid in Acetic Acid Solution with 100% Sulfuric Acid Catalyst at 25OC
HtSOd,'
HzS04)
ml
mol
Dimer, %
2 hr
0.52 23.7 0.3 0.87 51.9 0.5 51.2 0.8 1.46 55.1 0.9 1.56 1.75 75.8 1. o 2.12 61.6 1.2 2.60 65.2 1.5 2.96 51.9 1.7 hll per gram of abietic acid. abietic acid.
en --
C
6 hr
20 hr
4 6 hr
47.9 59.4 57.0 67.1 67.1 71.2 68.1 67.7 75.0 70.8 70.2 67.9 71.4 70.9 73.6 69.9 Moles H*SO, per
57.5 68.6 73.3 68.6 74.8 76.8 78.1 77.8 mole of
0
0
A
.I
---
Bmzrnr lrooctanr Hrptanr
.2 .3 .4 *5 ML H2S04/qm. A b l r t l ~A c i d
-6
Figure 1. Dimer acid formation from abietic acid with sulfuric acid catalyst in hydrocarbon solvents
to dilute t h e sulfuric acid to 90, 80, and 70ojO. The results of this study are shown in Figures 2 and 3. The yields of dimer increased as the catalyst concentration was changed from 100 t o 80% aqueous (the total amount of HzSOapresent remained constant), but the reaction time must be extended for t h e lower concentrations (Figure 2). At 70% H2S04t h e final dimer content was not as high as t h a t obtained Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 2, 1972
157
II l
'I
,'" 0 &SO4
0
I -
I
I
I
I
I
20
40
'
l I
l
I
I
I
l
l
2.5
Figure 4. Dimer yield from abietic acid with varying amounts of 75y0HzSO4 in acetic acid at 44°C
80 I00 Time h r r
Figure 2. Formation of dimer acid from abietic acid with sulfuric acid catalyst of varying strengths with time in acetic acid
Table 111. Comparison of Dimerized Rosins by Various Procedures Dimer yield,
Rosin
I
esC ..
-
80
1.0 1.5 2.0 YL 7 5 % HgSO~lgrn.Abirtlc Acid
0.5
-I00
Solvent
Catalyst
WW gum* WG gum WW gum WW gum 0
%
CHC13 HzS04, 98% 60 CHC13 HzS04, 100% 57 Acetic HzS04, 98% 52 Acetic H2S04, 80% 43 Ball and ring softening point. Sinclair et al.
Acid no.
S.P."
146 . . . 111 . . . 154 142 153 136 (1970).
L
P
.E P 3
7570 -
65
t I
1
I
IO0
90
I
80 X HzS04(Aq)
I
'I
I
70
Figure 3. Variation of dimer content of final products from abietic acid with sulfuric acid catalyst strength in acetic acid
with 80 and 90% catalyst, but with sufficient time more dimer might have been formed. Figure 3 is a plot of final dimer content as a function of catalyst concentration. This indicates an optimum concentration of 86 to 87% H2S04 under the conditions used. The reaction time can be greatly reduced by increasing the temperature and quantity of catalyst. This is shown in the data of Figure 4 where 2 ml of 75% HzS04 catalyst per gram of abietic acid gave 80% dimer in 48 h r a t 44OC. The failure of t h e curve for 70% catalyst t o follow the general shape of the other curves in Figure 2 was due t o nonhomogeneity of the samples taken for analysis. The final dimer content was obtained by hydrolysis of t h e total mixture. Phase separation was also found t o occur in the 80% catalyst runs between the 20 h r and the final sampling and thus did not affect the shape of the curve. Analysis of the separating material in the 80% catalyst run indicated 91% dimer. I n addition to the higher yields of dimer obtained with acetic acid solutions, the 302-neutral-equivalent-acid contents of the products were consistently 90% or above. This is in comparison with acid contents of about 80% for materials prepared in chloroform. Decarboxylation appears to occur to 158 Lnd. Eng. Chem. Prod. Res. Develop., Vol. 1 1 , No. 2, 1972
a lesser degree in acetic acid. Table I compares acid contents of products having significant amounts of dimer present. Material recoveries were comparable in these effective systems. For comparison purposes, WW gum rosin was dimerized in glacial acetic acid using 98% H2S04 a t 25°C and 80% sulfuric acid at 4OOC. The results obtained on these products, the results obtained by Sinclair et al. (1970), and properties of dimerized rosin made in this work using chloroform are listed in Table 111.The softening points of those products prepared in acetic acid were considerably higher than the typical commercial polymerized rosin whereas the acid numbers are slightly higher. The sample prepared in chloroform must have undergone some decarboxylation to have the dimer content and low acid number found. Conclusions
The data published by Sinclair et al. (1970) and that found here indicate both the chloroform-sulfuric acid and the acetic acid-sulfuric acid polymerization systems to be more effective than the hydrocarbon-sulfuric acid systems investigated. The added effectiveness appears great enough to warrant serious consideration of either of these systems for commercial use. Literature Cited
ASTM E28-58T, Philadelphia, PA, 1958. Oae, S., Kitao, T., Kitaoka, Y., Chem. Ind. (London), 1961,
-p on,
LYL.
Parkin, Jr., B. A., Schuller, W. H., Lawrence, R. V., Ind. Eng. Chem. Prod. Res. Develop., 8, 304 (1969).
Sinclair. R. G.. Berrv. D. A.. Schuller, W. H., Lawrence, R. V., ibid.,'9,60 (1970)." ' Sinclair, R. G., Hinnenkamp, E . R., Boni, K. A., Berry, D. A., Schuller, W. H., Lawrence, R. V., J . Chromatogr. Sci., 9, 126 (1971). RECEIVED for review August 12, 1971 ACCEPTEDDecember 29, 1971
