Crotonaldehyde from acetaldehyde

It is often said that the property of acidity is manifest only in the presence of a base, and NMR studies of probe molecules became common following studies of amines by Ellis [4] and Maciel [5, 6] and phosphines by Lunsford [7] in the early to mid 80s. More recently, the maturation of variable temperature MAS NMR has permitted the study of reactive probe molecules which are revealing not only in themselves but also in the intermediates and products that they form on the solid acid. We carried out detailed studies of aldol reactions in zeolites beginning with the early 1993 report of the synthesis of crotonaldehyde from acetaldehyde in HZSM-5 [8] and continuing through investigations of acetone, cyclopentanone [9] and propanal [10], The formation of mesityl oxide 1, from dimerization and dehydration of... 

The mechanism of many condensation reactions has been shown to comprise consecutive ADDITION and elimination reactions, as in the base-catalyzed formation of fEj-but-2-enal (crotonaldehyde) from acetaldehyde, via 3-hydroxybutanal (aldol). The overall reaction in this example is known as the aldol condensation. 

With concentrated alkali, a resin is formed from repeated aldol condensations between aldol, crotonaldehyde and acetaldehyde. A similar condensation occurs with acetone (b.p. 56°), but the equilibrium mixture contains only a few per cent, of diacetone alcohol (III), b.p. 166° ... 

The commercial method consists in the oxidation of crotonaldehyde, which is itself prepared from acetaldehyde (see Section 111,141) ... 

Fig.4.36. Separation and chromatogram scan of 2,4-dinitrophenyIhydrazones of some carbonyl compounds. Peaks I - formaldehyde 2 = acetaldehyde 3 = furfural 4 = acrolein S = crotonaldehyde. (From ref. 68 with permission of Springer, Berlin.)...

Examples given in Expt 5.216 include the preparation of non-2-enoic acid starting from hexanal, but-2-enoic acid (crotonic acid) from acetaldehyde, and also hexa-2,4-dienoic acid (sorbic acid) starting from the conjugated aldehyde crotonaldehyde. 

As many as 70 products were at one time produced commercially from ethanol. Some of these downstream products are butanol, 2-ethyl hexanol, crotonaldehyde, butyraldehyde, acetaldehyde, acetic acid, butadiene, sorbic acid, 2-ethylbutanol, ethyl ether, many esters, ethanol-glycol ethers, acetic anhydride, vinyl acetate, ethyl vinyl ether, even ethylene gas. Many of these products are now more economically made from other feedstocks such as ethylene for acetaldehyde and methanol-carbon monoxide for acetic acid. Time will tell when a revival of biologically-oriented processes will offer lower-cost routes to at least the simpler products. 

If R=H (i.e., formaldehyde), reaction 7.6 occurs with high yield on both TiO and UO surfaces, while if R=CH3 or higher, the condensation of two aldehyde molecules competes and results in the formation of unsaturated higher aldehydes such as crotonaldehyde (CHjCH=CHCHO) from acetaldehyde (CH3CHO) (7.7) [63]. 

Zhang, S., Villalta, P.W., Wang, M., and Hecht, S.S. (2006) Analysis of crotonaldehyde- and acetaldehyde-derived l,N2-propanodeoxyguanosine adducts in DNA from human tissues using liquid chromatography electrospray ionization tandem mass spectrometry. Chem. Res. Toxicol, 19, 1386-1392. 

Ethyl-2-methylpyridine 164 (the educt in the industrial synthesis of nicotinic acid, see p 291) is formed from acetaldehyde or but-2-enal (crotonaldehyde) and aqueous NH3 in a similar process. 

In a process which is now largely of historical interest, 1-butanol has been produced from ethanol [64-17-5] via successive dehydrogenation (to acetaldehyde [75-07-0]) condensation (to crotonaldehyde [4170-30-3]) and hydrogenation. 

Organic constituents in the first wastestream totaled about 14,000 mg/L (acetaldehyde, acetal-dol, acetic acid, butanol-1, butyraldehyde, chloroacetaldehyde, crotonaldehyde, phenol, and propionic acid) and about 5200 mg/L inorganic constituents. The pH ranged from 4 to 6, and TDS ranged from 3000 to 10,000 mg/L. 

In contrast to the above, other reactions have been found to require base assistance by water in the rate-determining step, i.e. the water activity does appear in the rate law. The mechanism formulated for the condensation of acetaldehyde in sulfuric acid is given in equation (63), following on from the enolization of Scheme 7, subsequent dehydration to crotonaldehyde occurring as shown in Scheme 8. The ky k2, k3 and k 3 steps shown were all studied.246... 

The simple 1,2-dithiolenes, viz, 1,2-dithiolene (3, R H), 3-methyl-l,2-dithiolene (3, R Me) and the saturated derivative of the latter were detected by Takken and co-workers (2) with crotonaldehyde and butanedione as the starting materials. Ledl (33) identified 2-ethyl-4-methyl-l,3-dithiolene (4) in the reaction mixture containing propionaldehyde, hydrogen sulfide and ammonia, and the isomeric 2,4,5-trimethyl-l,3-dithiolane (5) was obtained by Sultan (29) from the reaction of acetaldehyde, aceto-in, and ammonium sulfide. 

Fig. 27. 50.1-MHz 13C MAS NMR spectra of acetaldehyde-/,2-13C2 on HZSM-5 that had been saturated with water. Crotonaldehyde (199, 160, 135, and 19 ppm) was produced selectively at 353-393 K. (Reprinted with permission from Munson and Haw (151). Copyright 1993 VCH Verlagsgesellschaft.)...

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