Alkenes with formic acid, catalysts

This is ordinary electrophilic addition, with rate-determining protonation as the first step. Certain other alkynes have also been hydrated to ketones with strong acids in the absence of mercuric salts. Simple alkynes can also be converted to ketones by heating with formic acid, without a catalyst.Lactones have been prepared from trimethylsilyl alkenes containing an hydroxyl unit elsewhere in the molecule, when reacted with molecular oxygen, CuCla, and a palladium catalyst. ... 

On the other hand, the linear ester 7 can be prepared as the major product by the carbonylation of a 1-alkene in the presence of a formate ester using Pd(Q) with dppb as a catalyst[12], The linear acid 8 is obtained as the main product by using Pd(OAc)2 or even Pd on carbon as a catalyst and dppb as a ligand in DME in the presence of formic acid or oxalic acid under CO pressure[13]. The linear ester 9 is obtained from a 1-alkene as the main product using PdCI2(Ph3P)2 coordinated by SnCl2[14]. 

On the basis of theoretical studies by Bach and co-workers,17 it was found that the nucleophilic 71-bond of the alkene attacks the 0-0 cr-bond in an Sn2 fashion with displacement of a neutral carboxylic acid. There are, however, some mechanistic anomalies. For example, a protonated peracid should be a much more effective oxygen transfer agent over its neutral counterpart, but experiments have shown only modest rate enhancements for acid catalysed epoxidation. Early attempts to effect acid catalysis in alkene epoxidation where relatively weak acids such as benzoic acid were employed proved unsuccessful.18 The picture is further complicated by contradictory data concerning the influence of addition of acids on epoxidation rates.19 Trichloroacetic acid catalyses the rate of epoxidation of stilbene with perbenzoic acid, but retards the rate of a double bond containing an ester constituent such as ethyl crotonate.20 Recent work has shown that a seven-fold increase in the rate of epoxidation of Z-cyclooctene with m-chloroperbenzoic acid is observed upon addition of the catalyst trifluoroacetic acid.21 Kinetic and theoretical studies suggest that the rate increase is due to complexation of the peroxy acid with the undissociated acid catalyst (HA) rather than protonation of the peroxy acid. Ab initio calculations have shown that the free energy of ethylene with peroxy-formic acid is lowered by about 3 kcal mol-1 upon complexation with the catalyst.21... 

Aryl and vinyl bromides and iodides have been employed most commonly, with 1-5 mol% Pd , and reaction temperatures ranging from ambient to 125 °C (equation 11). The Pd catalyst can be Pd(Pli3P)4 or the Pd species produced by in situ reduction of Pd. The alkene itself can serve as the reducing agent for Pd but the catalyst can also be produced by deliberate addition of a reducing agent, such as sodium borohydride, formic acid, or hydrazine. ... 

The acid-catalyzed hydrocarboxylation of alkenes (the Koch reaction) can be performed in a number of ways. In one method, the alkene is treated with carbon monoxide and water at 100-350°C and 500-1000-atm pressure with a mineral acid catalyst. However, the reaction can also be performed under milder conditions. If the alkene is first treated with CO and catalyst and then water added, the reaction can be accomplished at 0-50°C and 1-100 atm. If formic acid is used as the source of both the CO and the water, the reaction can be carried out at room temperature and atmospheric pressure.The formic acid procedure is called the Koch-Haaf reaction (the Koch-Haaf reaction can also be applied to alcohols, see 10-77). Nearly all alkenes can be hydrocarboxylated by one or more of these procedures. However, conjugated dienes are polymerized instead. Hydrocarboxylation can also be accomplished under mild conditions (160°C and 50 atm) by the use of nickel carbonyl as catalyst. Acid catalysts are used along with the nickel carbonyl, but basic catalysts can also be employed. Other metallic salts and complexes can be used, sometimes with variations in the reaction procedure, including palladium, platinum, and rhodium catalysts. The Ni(CO)4-catalyzed oxidative carbonylation with CO and water as a nucleophile is often called Reppe carbonylationP The toxic nature of nickel... 

Intermolecular reactions of species (69) with simple alkenes have received little attention. Recently, a study of the reaction of 5-ethoxy-2-pyrrolidinone with several 1,3-dienes in the presence of acid was published. When a mixture of ethoxylactam and 2,3-dimethylbutadiene is stirred in neat formic acid, the formates (73) and (74) are isolated as the main products in 43% yield. The bicyclic product (75) is obtained in only 16% (equation 38). If the reaction is carried out in benzene with p-toluenesulfonic acid as catalyst (75) is formed in 19% yield. Other dienes show similar behavior, producing bicyclic compounds as byproducts in low to moderate yields except for one or two cases, as illustrated with com-... 

The pivotal difference is the presence of excess formic acid, at least equimolar to added base, as the reducing agent The catalysis commences with an oxidative addition of the C(sp )—X bond of 148 to a paUadium(0) catalyst (148—>149). The thus-formed electrophiUc C(sp )—Pd(ll) complex 149 will then capture the alkene 150, followed by syn selective migratory insertion (149—>151). C(sp )—Pd(II) intermediates are normally prone to facile P-hydride elimination, yet no conformation-ally accessible C—H bond, neither at Cp nor at Cp-, is available in 151 (vide supra). Instead, salt elimination with formate (151—>152), followed by the extrasion of carbon dioxide, occurs (152 153). This detour establishes an alternative route to the o-alkyl palladium(ll) hydride intermediate 153, which could otherwise emerge from 151 if conventional P-hydride elimination were possible. Reductive... 

The exploitation of carbon dioxide (CO2) for the production of world-scale chemicals, such as formic acid, ° has industrial potential, as CO2 is a cheap and abundantly available Ci building block. Nevertheless, only a few reactions and catalysts enable the straightforward catalytic functionalization of industrially viable starting materials, such as alkanes and alkenes with CO2, to industrially relevant target molecules. 

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