Citral, purification

A) Purification of Citral.—In a 4-1. bottle are placed 1 1. of water, 1 kg. of crushed ice, 450 g. of anhydrous sodium sulfite (or an equivalent amount of hydrated sodium sulfite), 320 g. of sodium bicarbonate, and 270 g. (304 cc., 1.78 moles) of commercial citral (Note 1). A tightly fitting stopper is securely wired into place, and the bottle is shaken thoroughly for five to six hours. The solution, which contains very little unchanged citral, is extracted twice with 300-cc. portions of ether (Note 2). 

After cooling, the mixture is extracted twice with 200-cc. portions of ether to remove any material that has not reacted with the bisulfite. One-half of the aqueous solution is placed in the shaking extractor together with 650 cc. of ether. The calculated amount of 10 per cent aqueous sodium hydroxide (one mole of sodium hydroxide per mole of sodium bisulfite used) is now added as described for purification of the citral. Shaking is continued for fifteen minutes after the addition of the alkali is complete... 

Prior to the kinetic experiments, possible deactivation phenomena of the catalytic system were checked by recycling experiments with prenal and citral as substrates. These results provide not only important hints on the form of the rate equation, but also on which reaction is convenient for long-term investigations in the loop reactor. After the reaction, the aqueous and organic phases were separated and the catalyst phase was reused without further purification. Results on the hydrogenation of prenal are shown in Fig. 7. The reaction rate clearly decreases if the catalyst phase is reused. According to GC analysis and H-NMR studies, this can be attributed to the fact that the product of the reaction, prenol, is highly soluble in water. Consequently, a simple phase... 

Natural aroma chemicals Isolation and purification via physical processes Citral from lemon grass oil, eugenol from cloves, menthol from Mentha species... 

Chromium trioxide, 21, 6 24, 39, 76 Cinnamic acid, 20, 77 22, 26 24, 21 Cinnamoyl chloride, 20, 77 24, 21 Citral, bisulfite compound, 23, 78 purification of, 23, 78 Claisen condensation, with acetone and ethyl formate, 27, 92 with ethyl oxalate and ethyl succinate, 26,42... 

Pseudoionones are produced commercially by the aldol condensation of citral and acetone catalyzed by aqueous or ethanolic solutions of bases. However, these liquid catalysts have potential problems related to undesirable side reactions (self-condensation of citral and secondary reactions of pseudoionones), catalyst separation and disposal (the catalyst caimot be reused and causes serious damage to the environment) as well as purification steps, which are laborious and costly [268]. These homogeneous processes also require a large excess of acetone, typically 10-20 moles per mole of citral, for a satisfactory yield, and a large and costly plant is needed for commercial production. 

Commercial production of vitamin A, as well as other carotenoids, typically proceeds via the key intermediate pseudoinone (48) [21], which is prepared by condensation of acetone with the natural product citral. This commercial procedure has the drawback of relying on the purification of citral from lemon grass oil. In an attempt to relieve this dependence on citral, Kimel and coworkers at Hoffmann-La Roche developed an alternative fuUy synthetic route to pseudoinone (48) involving multiple Carroll rearrangements (Scheme 8.18) [22]. 

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