Azelaic half-aldehyde

The aqueous solution (about 180 cc.) of non-volatile products from the steam distillation is cooled to room temperatime, filtered to remove a little insoluble material, and then cooled in ice water. The somewhat impure azelaic half aldehyde (3.33 g., or 76%) which separates is collected, dried, and extracted with 400 cc. of boiling light petroleum (b.p. 40-60°) in which all but 0.6 g., identified as the trimer of the aldehyde acid, dissolves. When the petroleum solution is cooled in ice-salt mixture, the semialdehyde separates as plates which, after several re-crystallizations from 50 parts of warm water, yields 1.6 g. of pure azelaic aldehyde acid as colorless rhombic plates melting at 38°. 

These studies showed that azelaic half aldehyde (IV), an intermediate product, is usually obtained in some quantity by decomposition of oleic acid ozonide. Reductive decomposition of the ozonide was then tried to preserve both aldehyde groups. Sodium sulfite as the reducing agent gave the first successful result. Azelaic half aldoxime (VI) could then be easily obtained from azelaic half aldehyde (IV) and hydroxylamine. Finally, co-aminononanoic acid (VII) was obtained by neutral reduction of azelaic half aldoxime (VI). 

Later experiments showed that w-aminononanoic acid (VII) can be prepared catalytically from azelaic half aldehyde (IV) without difficulty by action of ammonia and hydrogen. This simplified the process. 

The nonyl aldehyde coproduct of the azelaic half aldehyde is a useful intermediate after being transformed into the corresponding alcohol, acid, or amine, it is a raw material for plastics. Several years ago, I. Sakurada, Kyoto University, the inventor of Vinylon, found that when nonyl aldehyde is used instead of formalin for acetalization of poly (vinyl alcohol), the properties of Vinylon yarns are considerably improved, especially in elastic recovery. 

KIOJ in 300 ml. of N sulfuric acid at 20° is added rapidly to a solution of 8 g. of (4) in 400 ml. of 95% ethanol at 40°. After 10 min. the colorless solution is cooled to 15°, water is added to dissolve precipitated potassium sulfate, and extraction with ether and steam distillation affords 3.3 g. (76%) of pelargonic aldehyde. The aqueous solution is filtered, and cooled in ice and crude azelaic half-aldehyde (6) is collected (3.3 g., 76%). Extraction with petroleum ether leaves a residue of trimer (0.5 g.), and purification through the semicarbazone affords 1.5 g. of the pure aldehyde-acid (m.p. 38°). 

The dimerization of half esters to l,n-diesters is also called Brown-Walker electrolysis. Thereby valuable intermediates for the synthesis of medium-sized rings or l,n-difunctionalized compounds can be prepared (Table 2, entry 4). This reaction is also of industrial interest since in this way sebacic acid can be prepared from adipic acid half ester. This process has been scaled-up in Germany, the USSR and Japan, and yields as high as 93% have been reported. Reaction conditions and yields for the coupling of other half esters have also been studied in detail. 1, -Polyethylene- or polydifluoromethylene-dicar-boxylic acids are reported to be formed by electrolysis of azelaic acid or perfluoroglutaric acid. Ketocarboxylic acids can be coupled to 1,4-, 1,6- or 1,14-diketones (Table 2, entries 9 and 10). Aldehydes must be dimerized in the form of their acetals to obtain good yields, as has been shown for (17) and (18). The arrow on (10)-(18) indicates the location of dimerization, along with the yield and reaction conditions. 

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See also in sourсe #XX -- [ ]

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