Elaidin reaction

The course of the elaidinization reaction can be followed graphically by means of the critical demixing temperature of the oil, using, for example, aniline as a solvent. According to Dahmen the rise in the critical demixing temperature is approximately proportional to the degree of elaidinization (cf. Fig. 85). 

The course of the elaidinization reaction can be followed by dilatometric measurements (11), consistency determinations (12), by means of critical demixing temperatures, using aniline or triacetin as a solvent (9), or, more directly, by infrared spectrophotometry (13). 

In general, the presence of fatty acid groups in the phosphoHpid molecule permits reactions such as saponification, hydrolysis, hydrogenation, halogenation, sulfonation, phosphorylation, elaidinization, and ozonization (6). 

Several active elaidinization catalysts are known76 of which selenium and sulphur dioxide certainly are the most attractive ones. With liquid sulphur dioxide optimum results are obtained under relatively mild conditions (iio-ii5°C, 35 atm., 3 h) the low reaction temperature is favourable for the application of the hardened oils in the margarine industry. 

In 1989, a different approach was published by Orito [60], in which elaidinization ((Z) —> ( ) double bond isomerization) is used to obtain ( )-MNA from a (Z, )-mixture ofdiastereomers (Scheme 4.6). Gannet had observed that the iodine-induced photoisomerization of the methyl ester of MNA (48) gave only a 7 3 ( /Z) mixture [59], but Orito obtained a better diastereomeric ratio (8 1) using nitrous acid. Remarkably, no double-bond migration to form the more stable trisubstituted olefin was observed. This discovery paved the way to a very simple and general synthesis of the acidic component of capsaicinoids. Thus, a Wittig reaction of the phosphonium salt of a 6-bromohexanoic acid (49) with isobutyraldehyde (SO) afforded a 1 11... 

For nondrying oils only those isomerization processes are of value which bring about an increase of the melting point (hardening) of the oils. This type of reactions includes elaidinization cis-trans conversions) of esters of oleic acid and other mono-unsaturated fatty acids. 

In both these isomerization processes liquid sulfur dioxide has been found to be an active catalyst. The optimum reaction conditions, and particularly the temperature, are sufficiently different to allow a completely selective performance of each type of transformation. This is of special interest in the processing of semidrying oils, such as soybean, cod-liver, and herring oils 1,2). It is possible to harden these oils by heating them in the presence of liquid sulfur dioxide to 110 to 115° at a pressure of 35 atm. for 2 to 3 hrs. Crystallization of the partly solidified reaction products yields a solid fraction, containing the elaidinized mono-unsaturates, and a liquid portion, which is enriched in the poly-unsaturates and shows improved drying properties, A further improvement of this liquid portion can be achieved by... 

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