Valeraldehyde synthesis

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

Scheme 3. Synthesis ofthe key intermediate en route to (+)-boronolide based on a catalytic, asymmetric direct aldol addition reaction of 2-hydroxyacetylfuran and valeraldehyde.

Conjugated diolefins react in an interesting fashion with synthesis gas. The major overall reaction consists of the hydrogenation of one double bond and the hydroformylation of the other. Thus, for example, butadiene gives n-valeraldehyde. The reaction may proceed by 1,4-hydrogen addition followed by isomerization and hydroformylation ... 

The remaining 30 percent of 1-butene is divided among several uses. About 10-15 percent of the 1-butene is polymerized in the presence of a Ziegler-type catalyst to produce polybutene-1 resin. The markets for this resin are pipe, specialty films, and polymer alloys. Approximately the same volume of 1-butene is reacted with synthesis gas in an oxo reaction to produce valeraldehydes. These C5 aldehydes are then hydrogenated to amyl alcohols or oxidized to valeric acid. Amyl alcohols are consumed in the production of lube oil additives and amyl acetate and in solvent uses. Valeric acid goes into lubricant base stocks and specialty chemicals. 

Metallated methylenecyclobutane has been used as an isoprene equivalent in terpene synthesis. Methylenecyclobutene has been metallated with butyl-lithium and tetramethylethylenediamine. Reaction of the ambident anion (384) with electrophiles gives a mixture of positional isomers. The ratio of the isomers can be controlled by variation of solvent and temperature in this reaction and the cyclobutene ring in the products can then be opened thermally to dienes. This method has been applied to a synthesis of a component of the Ips confusus pheromone. Reaction of (384) with iso-valeraldehyde gave 30 % of the cyclobutene (385) which was isomerized to (386) by heating at 150°C. 

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