Of crotonic acid

Examples of prolate near-symmetric rotors are the s-trans and s-cis isomers of crotonic acid, shown in Figure 5.8, the a axis straddling a chain of the heavier atoms in both species. The rotational term values for both isomers are given approximately by Equation (5.37) but, because A and B are different for each of them, their rotational transitions are not quite coincident. Figure 5.9 shows a part of a low-resolution microwave spectmm of crotonic acid in which the weaker series of lines is due to the less abundant s-cis isomer and the stronger series is due to the more abundant s-trans isomer. 

Figure 5.9 Part of the microwave spectmm of crotonic acid. (Reproduced, with permission, from Scharpen, L. H. and Laurie, V W., Analyt. Chem., 44, 378R, 1972. Copyright 1972 American Chemical Society)...

The synthesis of key intermediate 12, in optically active form, commences with the resolution of racemic trans-2,3-epoxybutyric acid (27), a substance readily obtained by epoxidation of crotonic acid (26) (see Scheme 5). Treatment of racemic 27 with enantio-merically pure (S)-(-)-1 -a-napthylethylamine affords a 1 1 mixture of diastereomeric ammonium salts which can be resolved by recrystallization from absolute ethanol. Acidification of the resolved diastereomeric ammonium salts with methanesulfonic acid and extraction furnishes both epoxy acid enantiomers in eantiomerically pure form. Because the optical rotation and absolute configuration of one of the antipodes was known, the identity of enantiomerically pure epoxy acid, (+)-27, with the absolute configuration required for a synthesis of erythronolide B, could be confirmed. Sequential treatment of (+)-27 with ethyl chloroformate, excess sodium boro-hydride, and 2-methoxypropene with a trace of phosphorous oxychloride affords protected intermediate 28 in an overall yield of 76%. The action of ethyl chloroformate on carboxylic acid (+)-27 affords a mixed carbonic anhydride which is subsequently reduced by sodium borohydride to a primary alcohol. Protection of the primary hydroxyl group in the form of a mixed ketal is achieved easily with 2-methoxypropene and a catalytic amount of phosphorous oxychloride. 

Vinylacetio acid is available from Toltyokasei Company, Ltd., Japan or from Fluka AG, Buchs, Switzerland. Commercial material, which shows about 3% of crotonic acid [2-Butenoic acid, (A)-] in its proton magnetic resonance spectrum, was distilled at 90-92° (40-43 mm.) prior to use. 

Self-Test 10.10A The pH of a 0.20 m aqueous solution of crotonic acid,... 

C I l5CO()[ I, which is used in medicinal research and in the manufacture of synthetic vitamin A, is 2.69. What is the Ka of crotonic acid ... 

Rao and colleagues [80] reported the first example of baker s yeast-catalyzed Diels-Alder reaction. Reactions of cyclopentadiene (1) with dienophiles 119 and 120 (Scheme 4.21) in the presence of baker s yeast at pH 7.2 afford prevalently the exo adduct with the exception of crotonic acid 120a. 

Carboxy-l-methylethyl)amino]-5-trifluoromethylaniline (120) gave 2-phenyl-7-trifluoromethylquinoxaline (122), probably by loss of crotonic acid and water from the unisolated intermediate (121) (neat BzCHO, 155°C, 3 h 82% note that no isomer was detected). " ... 

The Knoovenagol method (p T 161 ) gives high yields of crotonic acid. The allylic bromination uses N3S in CCl and the ylid (9) is stable enough to be isolated. 

When the epoxy-isobutenyl ester of crotonic acid is treated with the Cp2ZrCl2/AgC104 Lewis acid, the epoxide is opened by intramolecular assistance of the ester carbonyl group, giving a dioxolenium cation (Scheme 8.49). This species is a highly electrophilic Diels—Alder dienophile that reacts with a range of dienes. THF deactivates cationic zirconocene species and is therefore not tolerated as a solvent [89]. 

The conversion experience is found in Ingold s response to a paper presented by Robinson at the Chemical Society in the summer of 1925 and sent to Ingold before its publication in 1926. Robinson s paper, written with J. Allen, A. E. Oxford, and John C. Smith, classified conjugated systems into nine categories of reactants, two of them "anionoid" and the rest "cationoid." "Crotonoid" and "crotenoid" were two of the nine types. This was a detailed and cumbersome classification, based on studies of crotonic acid, amino acids, and their salts, in which crotenoid was an instance of anionoid (electron donor) reaction and crotonoid of cationoid (or electron acceptor) reaction. 

Portion of 100 MHz NMR spectrum of crotonic acid in CDCI3 is given below. The upfield part of the spectrum, which is due to the methyl group, is less amplified to fit the page. 

A substance which proved to be a polymer of crotonic acid, also possessing the formula (C4HeO])n that has just been mentioned, has been extracted from certain purple bacteria. It is formed during the metabolism of some photosynthesizing bacilli and occurs as a reduction product of compounds of carbohydrate nature. 

Crotonic acid is an example of an a(S-unsaturated acid, whilst vinylacetio acid is a (3y-unsaturated acid. Upon heating the latter with a solution of an alkali hydroxide at 100° or with sulphuric acid, it passes almost completely into the forrper. Actually an equilibrium mixture is produced containing 98 per cent, of crotonic acid ... 

The oxycarbonylation of propene under the same conditions results in the formation of crotonic acid as the major product instead of the more valuable methacrylic acid.439 When the oxycarbonylation of ethylene or terminal alkenes is carried out in anhydrous alcoholic solvents instead of acetic acid, dialkyl succinates and /3-alkoxy esters are the major products (equation 173).441,442... 

A. sec-Butyl crotonate. In a 2-1. round-bottomed flask are placed 258 g. (3 moles) of crotonic acid (Note 1), 370 g. (5 moles) of sec-butyl alcohol in which has been dissolved 6-7 ml. of concentrated sulfuric acid, and 300 ml. of benzene. A few boiling chips are added, and the flask is fitted with a suitable water separator (Note 2) in the top of which is placed a reflux condenser. The mixture is heated under reflux for about 12 hours or until no further separation of aqueous phase occurs. About 65 ml. of water is collected. The cooled reaction mixture is diluted with 200 ml. of ether, washed with 10% sodium carbonate solution... 

Eastman Organic Chemicals practical grade of crotonic acid (containing 10% water) was used by the checkers without further purification. 

Iodonium salts 60 react with cyanide anion affording the cyano derivatives of crotonic acid 61 as single isomers retaining the initial configuration of the phenyliodonium tosylate (Scheme 28) [51]. 

It has been demonstrated that optically active oxetanes can be formed from oxazolidinone 92, a crotonic acid moiety functionalized with Evans chiral auxiliary (Scheme 18) <1997JOC5048>. In this two-step aldol-cyclization sequence, the use of 92 in a deconjugative aldol reaction, with boron enolates and ethanal, led to formation of the syn-aldol 93. This product was then converted to the corresponding oxetanes, 94a and 94b, via a cyclization with iodine and sodium hydrogencarbonate. This reaction sequence was explored with other aldehydes to yield optically active oxetanes in similar yields. Unlike previous experiments using the methyl ester of crotonic acid, in an analogous reaction sequence rather than the oxazolidinone, there was no competing THF formation. 

Further, Maxted (36) studied the influence of several sulfur compounds on the activity of platinum black for the hydrogenation of crotonic acid in the liquid phase. He noticed that between 15 and 50°C the toxicity remains constant for a sulfur compound, pointing out the irreversibility of sulfur adsorption. Conversely, the toxicity of various compounds increases with the molecule size. For molecules containing two sulfur atoms, losing all freedom of rotation through this double adsorption, the toxicity is less than for molecules of the same length containing only one atom of sulfur. 

Fig. 1.31. The Wohl-Ziegler bromination of crotonic acid methyl ester D exclusively supplies the bromocrotonic ester G. However, vinyl acetic acid ester C and NBS exclusively yield the dibromo addition product B under Wohl-Ziegler conditions. Here, NBS acts as a Br2 source for addition rather than substitution. The fact that vinyl acetic acid ester and NBS do not react likewise to yield the bromocrotonic ester G is due to an electronic effect discussed in the text.

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