Abietic acid disproportionation

Abietane skeleton, 375, 378 Abietic acid disproportionation, 375 loss in manufacture of pine pitch, 377 oxidation, 375 structure, 371... 

Fig. 3. Resin acids in rosin sizes, R = CH(CH2)2- The rosin acids are represented here as abietic acid [514-10-3] (1) and levopimaric acid [79-54-9] (2). In rosin there are other isomers and disproportionation products. The product of reaction with fumaric acid (3) is levopimaric acid— fumaric acid adduct...

The paper industry uses large amounts of the sodium salt of rosin as paper size, which accounts for the greatest single use of rosin. The synthetic rubber industry is the second most important user of rosin. In making styrene-butadiene rubber, disproportionated rosin soaps are used alone or in combination with fatty acid soaps as emulsifiers in the polymerization process. Disproportionation decreases the number of double bonds in the abietic acid of the rosin, making a more stable material. 

On aging, and more rapidly on heating, abietic acid is oxidized first by disproportionation (i.e., without need of oxygen) to dehydroabietic acid (structure 1) and then (but only if exposed to oxygen) to 7-ketodehydroabietic acid (structure 2). The skeletal frequencies of dehydroabietic acid lie at 1110, 1130, and 1175 cm"1 (14),... 

Sample 7 contained more than 20% unchanged abietic acid, more than 50% dehydroabietic acid, but very little 7-ketodehydroabietic acid. This composition is not expected of a pine pitch but of a pine resin that has been through slow disproportionation in an anaerobic environment. This residue is therefore that of a pine resin added to wine to make the retsina for which Greece was noted in antiquity as it is today. Sample 1 contained only 1% unchanged abietic acid, but more than half of the dehydroabietic acid was oxidized to 7-ketodehydroabietic acid, a finding that indicates the presence of air during the preparation of the pitch. 

Activity increases with temperature until disproportionation of abietic acid becomes significant. Therefore, it is generally preferred that the temperature profile consist of a steep ramp in the range of solder melting, especially for alloys that melt near or above 300°C. Typically, the ramp of a reflow temperature profile increases slowly to allow solvents to evolve, has a soak plateau between the solvent boihng point and solder melting temperature, and has a rapid ramp to the solder melting temperature. 

Continuous polymerization in a staged series of reactors is a variation of this process (82). In one example, a mixture of chloroprene, 2,3-dichloro-l,3-butadiene, dodecyl mercaptan, and phenothiazine (15 ppm) is fed to the first of a cascade of 7 reactors together with a water solution containing disproportionated potassium abietate, potassium hydroxide, and formamidine sulfinic acid catalyst. Residence time in each reactor is 25 min at 45°C for a total conversion of 66%. Potassium ion is used in place of sodium to minimize coagulum formation. In other examples, it was judged best to feed catalyst to each reactor in the cascade (83). 

On the other hand, not only initial colour but colour change (discolouration) of the resin under UV light and heat is important. Colour retention of a resin is related to the chemical stability and increases as the degree of non-aromatic conjugated unsaturation of the resin molecule decreases. Thus, for rosins a high level of abietic-type resin acids lead to relatively unstable resins. Hydrogenation and disproportionation as well as esterification provide improved stability and colour retention to rosins. 

Conventional anionic emulsifiers are alkyl sulfates, alkyl sulfonates, aralkyl sulfonates, soaps of saturated or unsaturated fatty acids and alkaline disproportionated or hydrogenated abietic or tall oil acids (14). 

Rosin. Rosin is used mainly in some modified form. Because the abietic-type acids in rosin each contain a carboxyl group and double bonds, they are reactive and can be used to produce salts, soaps, esters, amines, amides, nitriles, and Diels Alder adducts and they can be isomerized, disproportionated, hydrogenated, dimerized, and polymerized. When destructively distilled, rosin produces a viscous liquid, termed rosin oil, used in lubricating greases. 

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