Crotonaldehyde production

If, instead of performing the reaction under basic conditions, the ethanal is treated with an acid, a similar result may be obtained to form the enol, which in turn attacks the protonated (and so activated) carbonyl compound to form initially the aldol, and then the crotonaldehyde, product. It is more usual for the dehydration step to occur under acidic conditions. 

Figure 2.7 Crotyl alcohol selox over Pd/AI Oj is a strong function of support morphology and Pd oxidation state, with atomically dispersed Pd + centers obtained over mesoporous alumina offering maximum crotonaldehyde production. (Adapted with permission from Ref [35]. Copyright Wiley-VCH Verlag GmbH. Co. KGaA.)...

Figure 2.10 (a) Cartoon of operand DRIFTS/MS/XAS reaction cell and resulting associated surface and gas-phase crotonaldehyde production under either crotyl alcohol or ox en environments over a partially oxidized Pd/meso-AljOj catalyst, (b) Cycling of surface Pd oxidation state under reducing/oxidizing reactant feed streams. (Reprinted with permission from Ref [158]. Copyright 2011, American Chemical Society.)... 

Normal butyl alcohol, propyl carbinol, n-butanol, 1-buianol, CH3CH2CH2CH2OH. B.p. 117 C. Manufactured by reduction of crotonaldehyde (2-buienal) with H2 and a metallic catalyst. Forms esters with acids and is oxidized first to butanal and then to butanoic acid. U.S. production 1978 300 000 tonnes. 

If acetaldehyde is warmed with a concentrated solution of an alkali hydroxide, it is converted into a resinous product resulting from repeated aldol condensations between aldol, crotonaldehyde and acetaldehyde. 

The aniline then reacts with the ap-unsaturated aldehyde by 1 4-addition the addition product, under the influence of strong acid, cyclises to form 1 2-dihydroquinaldine. The latter is dehydrogenated by the condensation products of aniline with acetaldehyde and with crotonaldehyde simultaneously produced ( .c., ethylideneaniline and crotonylideneaniline) these anils act as hydrogen acceptors and are thereby converted into ethylaniline and n-butyl-aniline respectively. 

Another principal use of ketene is in the production of sorbic acid [110-44-1] (80,81). In this process, which requires an acidic or manganese(II) catalyst, ketene adds to crotonaldehyde [123-73-9] (8) with subsequent conversion of the P-lactone and the polyester to sorbic acid (qv) (9). 

An excess of crotonaldehyde or aUphatic, ahcyhc, and aromatic hydrocarbons and their derivatives is used as a solvent to produce compounds of molecular weights of 1000—5000 (25—28). After removal of unreacted components and solvent, the adduct referred to as polyester is decomposed in acidic media or by pyrolysis (29—36). Proper operation of acidic decomposition can give high yields of pure /n j ,/n7 j -2,4-hexadienoic acid, whereas the pyrolysis gives a mixture of isomers that must be converted to the pure trans,trans form. The thermal decomposition is carried out in the presence of alkaU or amine catalysts. A simultaneous codistillation of the sorbic acid as it forms and the component used as the solvent can simplify the process scheme. The catalyst remains in the reaction batch. Suitable solvents and entraining agents include most inert Hquids that bod at 200—300°C, eg, aUphatic hydrocarbons. When the polyester is spHt thermally at 170—180°C and the sorbic acid is distilled direcdy with the solvent, production and purification can be combined in a single step. The solvent can be reused after removal of the sorbic acid (34). The isomeric mixture can be converted to the thermodynamically more stable trans,trans form in the presence of iodine, alkaU, or sulfuric or hydrochloric acid (37,38). 

The ketene—crotonaldehyde route through polyester with various modifications and improvements is reportedly practiced by Hoechst Celanese, Cheminova, Daicel, Ueno, Chisso, Nippon Gohsei, and Eastman Chemical Company. Differences in thein processes consist mosdy in the methods of polyester splitting and first-stage purification. Production of the potassium salt can be from finished sorbic acid or from a stream in the sorbic acid production route before the final drying step. Several patents on the process for producing sorbic acid and potassium sorbate from this route are given in the hterature. 

The earhest commercial route to -butyraldehyde was a multistep process starting with ethanol, which was consecutively dehydrogenated to acetaldehyde, condensed to crotonaldehyde, and reduced to butyraldehyde. In the late 1960s, production of -butyraldehyde (and isobutyraldehyde) in Europe and the United States switched over largely to the Oxo reaction of propylene. 

The limitations of the reaction consist in the nonavailability of suitably substituted 2-buten-l-ones (78), in the moderate yields (usually up to 40%) and poor purity of the products, and in the fact that in most cases at least three substituents are required in positions 2, 4, and 6 of the resulting pyrylium salt for its isolation. Ethylidene-acetone (78, R = Me, R = H) and crotonaldehyde (78, R = H, R =Me) failed to yield pyrylium salts on acetylation with AcCl-I-AlClg however, acetylation with AC2O+HCIO4 of jS-hydroxyaldehyde... 

As an example of the system in which parallel and consecutive reactions occur simultaneously, we have chosen the hydrogenation of crotonaldehyde, which may lead through two two-stage paths (via butyraldehyde and via crotyl alcohol) to the same final product, butanol... 

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... 

Dining distillation of 2-propanol recovered from the reduction of crotonaldehyde with isopropanol/aluminium isopropoxide, a violent explosion occurred. This was attributed to peroxidised diisopropyl ether (a possible by-product) or to peroxidised crotonaldehyde. An alternative or additional possibility is that the isopropanol may have contained traces of a higher secondary alcohol (e.g. 2-butanol) which would be oxidised during the Meerwein-Ponndorf reduction procedure to 2-butanone. The latter would then effectively sensitise the isopropanol or other peroxidisable species to peroxidation. 

Sorbic acid has been prepared from crotonaldehyde 1 5 or aldol6 and malonic acid in pyridine solution by hydrogen peroxide oxidation of the condensation product of crotonaldehyde and pyruvic acid 7 and by the action of alkali on 3-hydroxy-4-hexenoic acid,8 9 /3,5-disulfo-w-caproic acid,10 and parasorbic acid.1112... 

Cyclic hydrazides 411 react with acrolein, crotonaldehyde, and methyl vinyl ketone either by heating in a sealed tube at 150 °C or by refluxing in aqueous ethanol containing a catalytic amount of sodium hydroxide, to provide acceptable yields of the corresponding products 412 (Equation 57). Both possible cyclic tautomers are detectable <2002EJO3447, 2002PCJ598>. 

Thiophenes can also be obtained from aldehydes, as in the synthesis of thiophene itself from crotonaldehyde (2-butenal), or the production of 2,4-dimethylthiophene from propanal both reactions are carried out at high temperatures and in the presence of catalysts (Scheme 2).5... 

Intermolecular cross aldolization of metallo-aldehyde enolates typically suffers from polyaldolization, product dehydration and competitive Tishchenko-type processes [32]. While such cross-aldolizations have been achieved through amine catalysis and the use of aldehyde-derived enol silanes [33], the use of aldehyde enolates in this capacity is otherwise undeveloped. Under hydrogenation conditions, acrolein and crotonaldehyde serve as metallo-aldehyde enolate precursors, participating in selective cross-aldolization with a-ketoaldehydes [24c]. The resulting/ -hydroxy-y-ketoaldehydes are highly unstable, but may be trapped in situ through the addition of methanolic hydrazine to afford 3,5-disubstituted pyridazines (Table 22.4). 

A second similar synthesis, due to Doebner and Miller, leads to the formation of substituted quinolines. The simplest example is the production of quinaldine from aniline and paraldehyde by heating with concentrated hydrochloric acid. The course of the reaction is closely related to that of the Skraup synthesis by route II. There the aniline reacts with acrolein, here with crotonaldehyde, which is easily formed under the conditions which prevail ... 

An accessory proposal was Arthur Michael s hypothesis that many reactions proceed by addition, for example, a polymerization of acetaldehyde (CH3CH = O) in the presence of bases (OH) to an aldol (CH3CHOHCH2CHO), with subsequent loss of water to form crotonaldehyde (CH3CH = CHCHO). Michael, educated in America, Germany, and France, made use of Kekule s idea that two molecules may form a "polymolecule" or molecular compound, which, in turn breaks up to yield the final products.33 Lachman expressed fairly standard misgivings about this proposal of an intermediary and transition form "If we are going to explain reactions by means of addition products which we do not or cannot isolate, our explanation loses its definiteness. It becomes simply a possible explanation, and its conclusions are by no means binding."34... 

Crossed reactions of the two aldehydes under phase-transfer catalytic conditions with the intermediate thioacetates, which can be isolated under controlled reaction conditions [14], leads to the formation of three products [13], as result of retro-Michael reactions (Scheme 4.18). In the case of the reactions involving crotonaldehyde, the major product results from the reaction of the aldehyde with the released thiolacetic acid, with lesser amounts of the expected crossed reaction products (Table 4.23). In contrast, the reaction of acrolein with the thioacetate derived from crotonaldehyde produces, as the major product, the crossed cycloadduct. These observations reflect the relative stabilities of the thioacetates and the relative susceptibilities of acrolein and crotonaldehyde to the Michael reaction. 

The Skraup-type reactions proceed by the use of acrolein or 2-bromo-acrolein in the presence of mineral acids or with glycerol and sulfuric acid [52CI(L)562 60NKZ509], The quinaldine-type products are afforded by acetaldehyde, crotonaldehyde, or paraldehyde in the presence of hydrochloric acid (54JCS286). 

According to Scheme 6.2, the hydrogenation products for crotonaldehyde were butyraldehyde (SAL), crotyl alcohol (UOL), butanol (SOL) and cracking products only at trace levels. Selectivities to UOL, SAL and SOL were maintained from one cycle to the next [20]. 

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