Aldehydes crotonaldehyde

The reaction network for hydrogenation of the unsaturated aldehyde crotonaldehyde was studied extensively by Simonik and Beranek (20). They observed isomerization of the unsaturated alcohol to the saturated aldehyde at a reaction temperature of 433 K ... 

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. 

Unsaturated Aldehydes Acrolein (acrylic aldehyde) Crotonaldehyde (2-butenal) 2-Ethylcrotonaldehyde 2-Furaldehyde (furfural)... 

In industrial processes, formaldehyde, acetaldehyde and, to a lesser extent, acrolein are used as aldehydes crotonaldehyde can also be employed for the synthesis of pyridines. 

Reactions of the conjugated aldehydes, crotonaldehyde and 4-hydroxy-2-pentenal, with a C=C—C=0 bond system, in aqueous solution with thioglycollic add, either as its sodium salt or ethyl ester, give addition across the C=C bond. The 4-hydroxy-2-pentenal adduct cyclizes to the hemiacetal. 

CAUTION As described later in Chapter 2, the reaction of formaldehyde with hydrogen chloride has been shown to lead to the spontaneous production of the now known carcinogen te(chloromethyl) ether. In addition, other aldehydes (crotonaldehyde, acetaldehyde, acrolein, etc.) are also toxic [7], Toxicity limits for some representative compounds in air... 

Acetaldehyde (and other aldehydes containing at least one hydrogen atom in the a position) when treated with a small quantity of dilute sodium hydr oxide solution or other basic catalyst gives a good yield of aldol (p hydroxy-n-but3Taldehyde) (I), which readily loses water, either by heating the isolated aldol alone or with a trace of mineral acid, to form crotonaldehyde (II) ... 

Crotonaldehyde can be produced so cheaply on a commercial scale that its preparation in the laboratory is rarely undertaken. It is, however, included here as an illustration of the preparation of an unsaturated aliphatic aldehyde. 

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. 

Reactions with Aldehydes and Ketones. The base-catalyzed self-addition of acetaldehyde leads to formation of the dimer, acetaldol [107-89-1/, which can be hydrogenated to form 1,3-butanediol [107-88-0] or dehydrated to form crotonaldehyde [4170-30-3]. Crotonaldehyde can also be made directiy by the vapor-phase condensation of acetaldehyde over a catalyst (53). 

There is a significant difference in the toxicological effects of saturated and unsaturated afiphatic aldehydes. As can be seen in Table 6, the presence of the double bond considerably enhances toxicity. The precautions for handling reactive unsaturated aldehydes such as acrolein, methacrolein [78-85-3] and crotonaldehyde should be the same as those for handling other highly active eye and pulmonary irritants, as, for example, phosgene. 

Other aldehydes which have been used in the reaction are pro-panal, butanal, glycolaldehyde, 3-hydroxybutanal, and a number of phenylacetaldehydeand benzaldehyde derivatives. Whereas condensation of tryptophan with acetaldehyde takes place even at room temperature and pH 6.7, the reactions with chloral, chloroacetaldehyde, and crotonaldehyde fail entirely. 

To overcome these problems with the first generation Brmsted acid-assisted chiral Lewis acid 7, Yamamoto and coworkers developed in 1996 a second-generation catalyst 8 containing the 3,5-bis-(trifluoromethyl)phenylboronic acid moiety [10b,d] (Scheme 1.15, 1.16, Table 1.4, 1.5). The catalyst was prepared from a chiral triol containing a chiral binaphthol moiety and 3,5-bis-(trifluoromethyl)phenylboronic acid, with removal of water. This is a practical Diels-Alder catalyst, effective in catalyzing the reaction not only of a-substituted a,/ -unsaturated aldehydes, but also of a-unsubstituted a,/ -unsaturated aldehydes. In each reaction, the adducts were formed in high yields and with excellent enantioselectivity. It also promotes the reaction with less reactive dienophiles such as crotonaldehyde. Less reactive dienes such as isoprene and cyclohexadiene can, moreover, also be successfully employed in reactions with bromoacrolein, methacrolein, and acrolein dienophiles. The chiral ligand was readily recovered (>90%). 

It is noteworthy that even a separate treatment of the initial data on branched reactions (1) and (2) (hydrogenation of crotonaldehyde to butyr-aldehyde and to crotyl alcohol) results in practically the same values of the adsorption coefficient of crotonaldehyde (17 and 19 atm-1)- This indicates that the adsorbed form of crotonaldehyde is the same in both reactions. From the kinetic viewpoint it means that the ratio of the initial rates of both branched reactions of crotonaldehyde is constant, as follows from Eq. (31) simplified for the initial rate, and that the selectivity of the formation of butyraldehyde and crotyl alcohol is therefore independent of the initial partial pressure of crotonaldehyde. This may be the consequence of a very similar chemical nature of both reaction branches. 

Supported Lewis acids are an interesting class of catalysts because of their operational simplicity, filterability and reusability. The polymer-bound iron Lewis-acid 53 (Figure 3.8) has been found [52] to be active in the cycloadditions of a, S-unsaturated aldehydes with several dienes. It has been prepared from (ri -vinylcyclopentadienyl)dicarbonylmethyliron which was copolymerized with divinylbenzene and then treated with trimethylsilyltriflate followed by THF. Some results of the Diels-Alder reactions of acrolein and crotonaldehyde with isoprene (2) and 2,3-dimethylbutadiene (4) are summarized in Equation 3.13. 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

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... 

It has been shown previously how water-soluble rhodium Rh-TPPTS catalysts allow for efficient aldehyde reduction, although chemoselectivity favors the olefmic bond in the case of unsaturated aldehydes [17]. The analogous ruthenium complex shows selectivity towards the unsaturated alcohol in the case of crotonaldehyde and cinnamaldehyde [31]. 

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). 

Experiment 11.—A few drops of acetaldehyde, dissolved in about 2 c.c. of water, are heated in a test tube with 0-5 c.c. of dilute sodium hydroxide solution. A yellow colour develops and the acetaldehyde is converted by way of aldol into crotonaldehyde, which can be recognised in the boiling solution by its pungent odour. If acetaldehyde is heated with concentrated alkali solution yellow aldehyde resin is precipitated as a result of further condensation. 

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 unsaturated aldehyde (0.1 mol) is added to a two-phase system of thiolacetic acid (7.6, 0.1 mol) in aqueous NaOH (50%, 16 ml) and TBA-I (0.1 g, 0.27 mmol) in CH2CI2 (100 ml) over a period of ca. 30 min at 0°C. The mixture is stirred for 2.5 h at 0°C and then heated under reflux for 20 min. The organic phase is separated, diluted with Et20 (50 ml), washed with H20 (3 x 25 ml), and dried (MgS04). Evaporation of the solvent gives i-formyl-5-thiacyclohex-l-ene (41%) from acrolein and 1-formyl-4,6-dimethyl-5-thiacyclo-hex-l-ene (81%) from crotonaldehyde. 

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