Acrylic acid isomerization

Hogeveen138 measured apparent acidity constants of substituted /i-phenylthio-, /J-phenylsulfinyl- and / -phenylsulfonyl-acrylic acids (cis and trans) in 50% v/v ethanol. The p values for transmission through SCH=CH, SOCH=CH and S02CH=CH were 0.531, 0.389 and 0.320 respectively for the cis acids and 0.652, 0.282 and 0.331 for the trans acids. These results were discussed in considerable detail and compared with those of pertinent related systems. Little importance was attached to the small differences between p values for cis/trans isomers, and the relative transmissions were taken as the mean p values 0.59,0.34 and 0.33. The superior transmission of SCH=CH was attributed to greater polarizability. The values for pKJtrans) — pKJcis) of isomeric acids were also discussed. For the sulfonyl acids this is almost constant at 0.1 unit for the sulfinyl adds there is some variation about a mean value of 0.26 unit, and for the thio adds there is also some variation about a mean value of — 0.15 unit. The differing behavior of the three systems in this respect was explained in terms of hypothetical conformations and electrostatic interactions therein. 

Thus asymmetric diaryl cyclopropenones were converted to the isomeric acrylic acids 318/319 by aqueous Ni(C0)4 in a similar proportion to that obtained from the corresponding acetylenes by carbonylation with the same catalyst279, whilst in non-aqueous media carbonyls like Ni(C0)4, Co2(CO)8, or Fe3(CO)12 effected de-carbonylation278, 280) probably via metal-complexed intermediates, e.g. 

Hydroxypropionic Acid (3-HPA). Like the structurally isomeric lactic acid, 3-HPA constitutes a three-carbon building block with the potential of becoming a key intermediate for a variety of high-volume chemicals malonic and acrylic acids, methacrylate, acrylonitrile, 1,3-propanediol, and so forth.Thus, Cargill is developing a low-cost fermentation route by metabolic engineering of the microbial... 

The Diels-Alder reaction of a-phellandrene with acrylic acid derivatives has been examined, apparently superficially in contrast to the re-investigation of the reaction with benzalbisurethane, catalysed by BF3,Et20-CuBr. The 1,4-adducts (161 endo exo/31 63) may result effertively from the concerted [4 -I-2 ] addition involving the immonium ion (PhCH=NHC02Et) however, with the corresponding unsubstituted immonium ion, formal 1,3-addition to a-phellandrene occurs essentially via the isomerized a-terpinene and isoterpinolene to yield [(162) (163)/84 16]. ... 

The oxime derived from 2-furfural has been used for the first time as an electron-rich 1-azadiene by Kusurkar and Bhosale (91TL3199) (Scheme 16). Thus, 2-furfuraldoxime 60 undergoes at 120°C [4 + 2] cycloaddition to acrylonitrile, acrylic acid esters, and maleic anhydride to give stereoiso-meric cycloadducts 61 and 62. The isomeric fused pyridines obtained were not separated, but dehydrogenated to the corresponding furo[2,3-c]pyridine N-oxide derivatives. 

Oxidation of the allylic carbon of alkenes may lead to allylic alcohols and derivatives or a, 3-unsaturated carbonyl compounds. Selenium dioxide is the reagent of choice to carry out the former transformation. In the latter process, which is more difficult to accomplish, Cr(VI) compounds are usually applied. In certain cases, mixture of products of both types of oxidation, as well as isomeric compounds resulting from allylic rearrangement, may be formed. Oxidation of 2-alkenes to the corresponding cc,p-unsaturated carboxylic acids, particularly the oxidation of propylene to acrolein and acrylic acid, as well as ammoxidation to acrylonitrile, has commercial importance (see Sections 9.5.2 and 9.5.3). 

Metal-catalyzed reactions of CO with organic molecules have been under investigation since the late 1930s and early 1940s, when Roelen (/) discovered the hydroformylation reaction and Reppe (2) the acrylic acid synthesis and other related carbonylation reactions. These early studies of the carbonyla-tions of unsaturated hydrocarbons led to extremely useful syntheses of a variety of oxygenated products. Some of the reactions, however, suffered from the serious problem that they produced isomeric mixtures of products. For example, the cobalt-catalyzed hydroformylation of propylene gave mixtures of n-butyraldehyde and isobutyraldehyde. 

Butyl lithium (10 ml, 1.64 mol in hexane) was added under nitrogen to a stirred suspension of triphenyl-2-pyrrolidinoethylphosphonium bromide (7.2 g) in dry toluene (75 ml). After 0.5 h, ((E)-3-(6-(4-toluoyl)-2-pyridyl)acrylate, vide supra, (4.8 g) in toluene (50 ml) was added. The suspension, initially orange, became deep purple, then slowly faded to yellow during 2 h heating at 75°C. The cooled solution was diluted with ether (150 ml) and treated with hydrochloric acid (50 ml, 2 mol). The aqueous phase was separated, washed with ether, and basified with potassium carbonate (ice) and extracted with ether. The mixture of isomeric esters obtained by evaporation was dissolved in ethanol (100 ml) containing sodium hydroxide solution (20 ml, 1 mol) and partially evaporated on the steam bath under reduced pressure for 5 min. The residual aqueous solution was neutralized with sulfuric acid (20 ml, 0.5 mol) and evaporated to dryness. The solid residue was extracted with hot isopropanol (3x50 ml) and the extracts were concentrated until crystallization commenced. The (E)-3-(6-(3-pyrrolidino-l-(4-tolyl)prop-l-(E)-enyl)-2-pyridyl)acrylic acid, melting point 222°C (dec. recrystallization from isopropanol) was obtained. 

A haloalkene that contains a stereogenic C=C double bond can usually be coupled with alkenes via the Heck reaction without isomerization. This is illustrated with the three reaction pairs in Figure 16.36. As can be seen, both the as- and the /raw-configured iodoalkenes react with acrolein or methyl vinyl ketone or acrylic acid methyl ester with complete retention of the C=C double bond configuration. These coupling reactions are thus stereoselective and— when considered as a pair—stereospecific. 

Among the classic examples is the coupling-cyclization of alkynes with Z-f)-bromo acrylic acid derivatives invented by Negishi and Kotora [110] as a sequential access to the y-alkylidcncbulcnolide 140 in excellent yield (Scheme 53). The constitutional isomeric a-pyranone 141 is only formed in 4% yield. 

Acid hydrolysis of the simpler olefinic nitriles to olejinic acids occurs without appreciable migration of the double bond. Acrylic acid is made by hydrolysis of acrylonitrile with sulfuric acid (78%). Concentrated hydrochloric acid is used to convert allyl cyanide to vinylacetic acid (75-82%). Similarly, 3"pentenonitrile furnishes a 70% yield of 3-pen-tenoic acid, but the isomeric 2-methyl-3-butenonitrile is not hydrolyzed under the same conditions. The alkaline hydrolysis of higher-molecular-weight branched a, -olefinic nitriles gives mixtures of isomeric and /S,7-olefinic acids. ... 

An H-atom on nitrogen significantly affects the reactivity of 71 [42], By contrast, the acrylic acid amide containing a phenyl group on the N atom 87 underwent RCM, and treatment of 89 with complex 71 resulted in exclusive olefin isomerization (Eqs. 12.35 and 12.36). 

N-Arylcyclopropenimines 363 having a nucleophilic moiety at the o-position of the aromatic ring can isomerize to the five-membered heterocycles 364 in a process reminiscent of the conversion of cyclopropenones into acrylic acid derivatives (Section VI.B.S)" ... 

Allyl alcohol is isomeric with propylic aldehyde and with acetone. Being an unsaturated compound, it is capable of forming products of addition with Cl, Br and 1, etc., which are isomeric or identical with products of substitution obtained by the action of the same elements upon glycerol. Oxidizing agents convert it first into acrolein, acrylic aldehyde, CsH40, and finally into acrylic acid. It does not combine readily with H, but in the presence of nascent H combination takes place slowly, with formation of propylic alcohol. 

The synthesis of isomeric thienothiophenes and benzothienothiophenes was successfully carried out starting from thiophenecarbaldehydes and their derivatives. Treatment of 2-mercapto-3-(3-thienyl)acrylic acid (37), prepared in quantitative yield from thiophene-3-carbaldehyde (38) and 2-thioxothiazolidin-4-one (39) through intermediate 40, gave with two equivalents of iodine in dioxane thieno[2,3- )]thiophene-2-carboxylic acid (41) (74SC29). 

F. Beilstein/ by the action of silver oxide on j8-iodopropionic acid obtained what he called hydracrylic acid, since it decomposed on heating into water and acrylic acid, and he formulated it C12H22O11. Its correct formula was found by W. Moldenhauer.2 Heintz believed that it was the same as Wislicenus s ethylene lactic acid, giving a zinc-calcium double salt, but Wislicenus thought they were different. The position was first clarified by Erlenmeyer, who showed that Wislicenus s ethylene lactic acid is hydracrylic acid. Wisli-cenus had found that paralactic acid is optically active (dextro-rotatory), whilst ordinary fermentation lactic acid is inactive, and he supposed that they should be represented by the same formula, CH3 CH(0H)-C02H. He says (1869) Thus is given the first certainly proved case in which the number of isomers exceeds the number of possible structures. Facts like these compel us to explain diflFerent isomeric molecules with the same structural formula by different positions of their atoms in space, and to seek for definite representations of these. ... 

Results similar, but less complete, than those reported for the above dienophile were reported for acrylic acid. The products isolated correspond to only one (X-46) of the two possible isomeric adducts that could be formed. Thermolysis to pyridinecarboxylic acid occurred as expected in about 50% overall yield. 

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