Crotonic acid, oxidation

CHa CHlCH CHO. Colourless lachrymatory liquid with a pungent odour. B.p. 104 "C. Manufactured by the thermal dehydration of aldol. May be oxidized to crotonic acid and reduced to crolonyl alcohol and 1-butanol oxidized by oxygen in the presence of VjOj to maleic anhydride. It is an intermediate in the production of l-butanol from ethanol. 

OL-crolonic acid. irans-crotonic acid. Colourless needles or large plates m.p. 72 "C, b.p. 180 C. Prepared by the oxidation of... 

The excess nitric acid is used in order to oxidize unchanged crotonic acid. Since hydrocyanic acid may be evolved the operation should be carried out under a hood. 

Acrylic acid (AA) and methacrylic acid (MAA) (purchased from Merck) are freed from inhibitor on a neutral aluminium oxid column and distilled. Acrylamide (AM) from Kebo, Stockholm, is recrystallized once from chloroform solution before use. Other monomers of analytical grade were purchased from Merck and used as received crotonic acid (CA), tiglic acid (TA), 3-methyl crotonic acid (3-MCA), and a-methyl cinnamic acid (oi-MCia) (Table 1). Benzophenone (analytical grade, Kebo) and acetone (spectroscope grade, Merck) were used as supplied. 

Chemical/Physical. Slowly oxidizes in air forming crotonic acid (Windholz et al., 1983). At elevated temperatures, crotonaldehyde may polymerize (NIOSH, 1997). 

Adams and Reifschneider 22 have reported ring opening and formation of 6-hydroxypyridine-2-crotonic acid by strong alkaline or acid hydrolysis of 6-hydroxy-4-quinolizone with ester groups in the 1-and 3-positions. However, hydrolysis with barium oxide affords the corresponding l-carbethoxy-3-carboxy-6-hydroxy-4-quinolizone. 

With the allylic intermediates, the introduction of oxygen is also possible and crotonaldehyde is one of the first oxygenated products to be formed. This molecule is not very stable, certainly not under reaction conditions, and will be further oxidized to crotonic acid or the relatively more stable furan. More severe oxidation will then result in the generation of maleic acid and its anhydride. 

A second-order dependence on crotonic acid has been observed in its Os(VIII)-catalysed oxidation with CAT in alkaline solution. The reaction rate varied linearly with the concentration of Os(VIII). A mechanism has been proposed.140 The kinetics of the ruthenium(III)-catalysed oxidation of the secondary amines with CAT in acidic medium have been obtained and mechanisms have been postulated.141 Uncatalysed and Ru(III)-catalysed oxidation of ethylenediamine, diethylenetriamine, triethylenete-tramine, aminoethylpiperazine, and isophoronediamine with CAT in HC1 solution showed a fractional dependence on the amine, hydrogen ions, and Ru(III), and it is independent of CAT concentration. TSNH2CI has been postulated as the reactive species and a mechanism has been suggested.142... 

The gas phase photooxidation of crotonaldehyde has been studied by Blacet and Volman.21 The product is crotonic acid, which condenses out of the system as soon as it is formed. The quantum yield of oxidation was found to increase steadily over the 3660-2380 A. wavelength range. At constant aldehyde pressure, the quantum yield was independent of oxygen pressure at 3130 and 2804 A. At 2537 A., however, the quantum yield increased rapidly with the oxygen pressure and a chain mechanism is likely. Addition of nitrogen at 2537 A. caused a marked decrease in the quantum yield indicating that excited molecules are involved. 

Osmium tetroxide is also a catalyst in the oxidation of the double bond by chlorates. Cis addition of hydroxyl groups takes place as is shown by the preparation of cis-l,2-cyclohexanediol from cyclohexene and the formation of the proper diastereoisomeric dihydroxy derivatives of maleic, fumaric, and 4-halocrotonic acids. Silver chlorate is preferred to potassium chlorate in the hydroxylation of crotonic acid. ... 

The aldehyde derived from the next higher hydrocarbon of the ethylene series, viz., the four carbon hydrocarbon, butene, is known as crotonic aldehyde because on oxidation it yields an acid known as crotonic acid. As there are two isomeric butenes due to the position of the double bond there will likewise be possible two isomeric aldehydes or butenals. 

Now the aldehyde which yields crotonic acid on oxidation, i.e., crotonic aldehyde, may be prepared by a synthesis which shows clearly that it must have the constitution of the first of these isomeric aldehydes, A 2-buten-al, CH3—CH = CH—CHO. 

Crotonic Acid from Crotonic Aldehyde.—We have previously shown (p. 169), that crotonic aldehyde is A2-butenal because of its synthesis by the aMol condensation of acetaldehyde. On simple oxidation crotonic aldehyde yields crotonic acid which must therefore have the constitution of A2-butenoic acid,... 

The unsaturated dibasic acids bear the same relation to the saturated dibasic acids, just considered, as the unsaturated mono-basic acids, acrylic acid, crotonic acid, etc. (p. 172), do to the saturated monobasic acids, acetic acid, etc. They are also the oxidation products of the unsaturated hydrocarbons, alcohols, and aldehydes just as oxalic and succinic acids are of the corresponding saturated compounds. As the simplest dibasic acid containing an ethylene unsaturated group will contain two carboxyl groups and also two doubly linked carbon atoms there must be at least four carbons in the compound. This compound will therefore correspond to succinic acid of the saturated series. Now succinic acid may be derived from either butane by oxidation or from ethane by substitution. Similarly the corresponding unsaturated acid may be derived from butene by oxidation or from ethene by substitution. All of these general relationships may be represented as follows ... 

Seven grams of crystallised crotonic acid in 50 c.c. of warm water are heated with 7 grams of mercuric oxide until complete solution takes place. The solution is then evaporated to about 25 c.c., cooled, and treated with 200 e.c. of absolute alcohol. The white precipitate is washed with alcohol and ether, and dried over calcium chloride. 

While alcohol oxidations have been the most common metal promoted reactions involving molecular oxygen, a number of other metal catalyzed oxidations of potential synthetic interest have been reported. Supported palladium catalysts are comparable to many soluble palladium catalysts in promoting the selective oxidations of alkenes and aromatics. 2-Butene was oxidized primarily to crotonic acid over Pd/C in water but methyl vinyl ketone and crotonaldehyde were also formed in significant amounts. When this oxidation was run in acetic acid the allyl acetates were the major products, particularly when a Pd/Al203 catalyst... 

One other important method of preparation had been used by two groups of workers it involved the direct oxidation of the crotonic acids by means of barium permanganate. Fittig and Kochs obtained by this process an anhydrous, crystalline, racemic dihydroxybutanoic acid (IVab) of m.p. 74-75° from crotonic acid, and a liquid dihydroxybutanoic acid (Illab) from isocrotonic acid. In 1904, Morrell and Hanson resolved the jS-methylglyceric acid (Illab) of Fittig and Kochs with quinidine and... 

A recent synthesis of (+)-sedridine (167) was reported in which a key step was the asymmetric cycloaddition of the nitrone 2,3,4,5-tetrahydropyridine A-oxide with an asymmetric crotonic acid derivative containing a chiral auxilliary [439], Sedridine has recently been isolated from the bark of Punica granatum [440],... 

Flammable liq. Lacrimatorl Vapors extremely irritating, mp —76.5" bp 104.0 djj 0.853 n 1.4384. Flash pt when anhydr 13 (55 F) (open cup). Explosive limits in air 2.95-15.5% v/v. Vapor density 2.41 (air = I)- Heat capacity 0.7cal/g/ C heat of vaporization 8.62 cal/mole. Commercial crotonaldehyde (93%) is stabilized with water (a solid phase separates out at —5 ). Readily resinifies to a dimer when pure, slowly oxidizes to crotonic acid. Soly in water (g/100 g) at 20p 18.1 at 5 19.2. Soly of water in croton-... 

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