Pyrolysis of Abietic Acid

Abstract

THE industrial utilizationof rosin includes processes in which the rosin is heated at various temperatures up to the distillation point at atmospheric pressures-e. g., in the preparation of metallic rosinates and rosin esters, the blending of rosin with synthetic resins, the purification of rosin by vacuum distillation, and the production of rosin oil. Since abietic acid is remarkably labile at temperatures above its melting point, the problem of the effect of temperature on rosin (and abietic acid) is of obvious importance in technical operations, where the acid function or the characteristic physical properties of rosin are of primary interest, and in the study of the chemistry of the resin acids. The progressive changes which occur as the acid is heated involve, as the temperature rises to the distillation point: isomerization, evidenced by the sharp decrease in melting point and change in optical rotatory power without change in acid or saponification number; loss of water; decarboxylation, with loss of carbon dioxide and monoxide; and finally complex decomposition yielding a large variety of open-chain and ring compounds. Although a considerable amount of data on both phases of the pyrolysis of the acid has accumulated from both industrial research (5) and purely scientific investigation (8), the information on the predistillation phenomena is especially difficult to correlate because of the unsystematic variation in the experimental conditions and the difference in properties of the rosins or acids used. The present article is offered as a systematic and more complete study of the decarboxylation, dehydration, and isomerization of Z-abietic acid from American wood rosin between its melting point and distillation temperature during arbitrarily chosen time and temperature intervals. All the experiments were carried out in pure nitrogen to avoid the more complex phenomena associated with the presence of oxygen.Preparation of Materials and Experimental Method Abietic acid was prepared according to the directions of Steele (11) from American wood rosin (I grade). The rosin was crystallized three times from 98 per cent acetic acid and then freed of the residual acid in va-.uo over solid sodium hydroxide. This product was

Pyrolyses of certain resin acids at 800.deg.

“…The pyrolyses of levopimaric acid, abietic acid, dehydroabietic acid, and methyl dehydroabietate were carried out by passing these compounds in benzene solution, with nitrogen, through a Vvcor tube filled with Vycor chips at 800°C and a contact time of 3.9 sec [calculated according to method of Balandin and Tolstopyatova (3) ]. As expected, considerable carbonaceous and gaseous products (10) were produced which were not collected or analyzed. The trapped pyrolyzates yielded about 25% (based on initial weight of material used) of gc analyzable compounds.…”

Primary Liquefaction of Coal by Hydrogenation

“…The high ethane contents of the gases from the glycol and acetamide experiments might be expected. The carbonyl groups in the vehicles [abietic acid (17), stearic acid, and ethyl dihydroabietate] were responsible for the high yields of carbon dioxide and monoxide in experiments 14, 31, and 35. It is interesting to note that carbon monoxide, but not carbon dioxide, was obtained in increased yield when acetamide was the vehicle.…”

Thermal Isomerization of Gum Rosin

“…the saponification number decreased from 173 to 145 in 8 hours and the acid number dropped from 168 to 127 during the same period. The difference between the acid number and the saponification number of rosin is probably due to the presence of the anhydrides of the resin acids (9). This indicates that about 10% of the acids present in the original rosin was converted to the anhydride by heating at 275°0.…”