Crotonization

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... 

Isocroionic acid, -crotonic acid, cis-croionic acid. Colourless needles m.p. 14 C, b.p. 169 C. Prepared by distilling -hydroxy-glutaric acid under reduced pressure. Converted to a-crotonic acid by heating at 180 C, or by the action of bromine and sunlight on an aqueous solution. 

Karathane A trade name for 2,4-dinitro-6-( 1 -methylheptyl)phenyl crotonate, CJ8H24N2O6, a compound which has both acaricidal and fungicidal activity. It is a red-brown oil of high boiling point, insoluble in water but soluble in most organic solvents. Karathane is used for the control of powdery mildew, and is nontoxic to mammals. 

Required Ethyl crotonate, 22-8 g. V-bromosuccinimide, 35 6 g. carbon tetrachloride, 40 ml. 

Dissolve 22-8 g. of ethyl crotonate in 40 ml. of dry carbon tetrachloride and add 35 6 g. of. V-bromosuccinimide. Heat the mixture under reflux for three hours. Cool to o and filter off the succinimide which is insoluble in cold carbon tetrachloride. Now shake the filtrate with water in a separating funnel, separate and dry the carbon tetrachloride layer with sodium sulphate. Filter through a fluted filter-paper into a Claisen flask and distil... 

This procedure is generally applied to the esterification of highly sensitive acids, which might otherwise undergo isomerisation. Thus in the example given, no ethyl crotonate is formed. 

Crotonic acid exists in cis and trans forms (compare maleie and fumaric acids) CH3—C—H CH3—C—H... 

Crotonic acid is an example of an a(3-unsaturated acid, whilst vinylacetic acid is a acid. Upon heating the latter with a solution of an... 

Mix together in a 250 ml. flask carrying a reflux condenser and a calcium chloride drying tube 25 g. (32 ml.) of freshly-distilled acetaldehyde with a solution of 59-5 g. of dry, powdered malonic acid (Section 111,157) in 67 g. (68-5 ml.) of dry pyridine to which 0-5 ml. of piperidine has been added. Leave in an ice chest or refrigerator for 24 hours. Warm the mixture on a steam bath until the evolution of carbon dioxide ceases. Cool in ice, add 60 ml. of 1 1 sulphuric acid (by volume) and leave in the ice bath for 3-4 hours. Collect the crude crotonic acid (ca. 27 g.) which has separated by suction filtration. Extract the mother liquor with three 25 ml. portions of ether, dry the ethereal extract, and evaporate the ether the residual crude acid weighs 6 g. Recrystallise from light petroleum, b.p. 60-80° the yield of erude crotonic acid, m.p. 72°, is 20 g. 

Examples of the Knoevenagel reaction with aldehydes are given under crotonic acid (111,145), P-n-hexylacrylic acid (111,144), sorbic acid (111,145) and furylacryUc acid (V,10). 

Methyl crotonate (IV) yields the valuable synthetic reagent methyl Y-bromo-crotonate (V) ... 

Methyl crotonate. Purify commercial crotonic acid by distiUing 100 g. from a 100 ml. Claisen flask attached to an air condenser use an air bath (Fig. II, 5, 3). The pure acid passes over at 180-182° and crystallises out on cooling, m.p. 72-73° the recovery is about 90 per cent. Place 75 g. of absolute methyl alcohol, 5 g. (2 -7 ml.) of concentrated sulphuric acid and 50 g. of pure crotonic acid in a 500 ml. round-bottomed flask and heat under reflux for 12 hours. Add water, separate the precipitated ester and dissolve it in ether wash with dilute sodium carbonate solution until effervescence ceases, dry with anhydrous magnesium sulphate, and remove the ether on a water bath. Distil and collect the methyl crotoiiato at 118-120° the yield is 40 g. 

Methyl y-bromocrotonate. Mix 36 g. of iV-bromosuccinimide, 40 g. of methyl crotonate and 60 ml. of dry, redistilled carbon tetrachloride in a 500 ml. round bottomed flask. Reflux ou a water bath for 12 hours by this time all the sohd should have risen to the surface of the liquid. Filter off the succinimide at the pump and wash it with a little dry carbon tetrachloride. Remove the solvent on a water bath and distil the residue under reduced pressure, preferably from a Widmer flask (compare Figs. II, 24, 4-5). Collect the methyl y-bromocrotonate at 77-78°/8 mm. the yield is 31 g. 

The carbonylation of some alkyl halides such as iodocyclohexane (911) can be carried out under neutral conditions in the presence of N,N,N.N-tetre,-methylurea (TMU), which is a neutral compound, but catches generated hydrogen halide. Molecular sieves (MS-4A) are used for the same pur-pose[768]. Very reactive ethyl 3-iodobutyrate (912) is carbonylated to give ethyl methylsuccinate (913) in the presence of TMU. The expected elimination of HI to form crotonate, followed by carbonylation, does not occur. 

The reaction of CO2 with allene using bis(dicyciohexylphosphino)ethane as a ligand affords a mixture of esters of methacrylic acid 17 and crotonic acid 18, and the lactone 19[12],... 

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