Anhydrous carbonylation

Evidence has been presented that iodide salts can promote the oxidative addition of Mel to [Rh(CO)2l2]"> the rate-determining step in the Rh cycle [12]. The precise mechanism of this promotion remains unclear formation of a highly nucleophilic dianion, [Rh(CO)2l3]2 , has been suggested, although there is no direct spectroscopic evidence for its detection. Possible participation of this dianion has been considered in a theoretical study [23]. An alternative nucleophilic dianion, [Rh(CO)2l2(OAc)]2 , has also been proposed [31,32] on the basis that acetate salts (either added or generated in situ via Eq. 7) can promote carbonylation. Iodide salts have also been found to be effective promoters for the anhydrous carbonylation of methyl acetate to acetic anhydride [33]. In the absence of water, the catalyst cannot be maintained in its active form ([Rh(CO)2l2]") by addition of Lil alone, and some H2 is added to the gas feed to reduce the inactive [Rh(CO)2l4]. ... 

We are now in a position, having considered the various model studies on individual reaction steps, to look more closely at what is observed in working catalytic MeOH and MeOAc carbonylation reactions. In some ways the anhydrous carbonylation of MeOAc to AC2O is easier to describe because, in the absence of HjO, there is little or no water gas shift chemistry competing with the main carbonylation cyde. 

Lithium aluminium hydride LiAlH is a useful and conveuient reagent for the selective reduction of the carbonyl group and of various other polar functional groups. It is obtained by treatment of finely powdered lithium hydride with an ethereal solution of anhydrous aluminium chloride ... 

The reactivity of 2-methylselenazole toward carbonyl compounds is the same as its thiazoie homolog. Reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride as catalyst gives 4-methyl-2-styrylselenazoie [m.p. 74-75 C (19)] (Scheme 43). 

Step 2 On reaction with hydrogen chloride m an anhydrous solvent the thiocarbonyl sulfur of the PTC derivative attacks the carbonyl carbon of the N terminal ammo acid The N terminal ammo acid is cleaved as a thiazolone derivative from the remainder of the peptide... 

Oxidative Carbonylation of Ethylene—Elimination of Alcohol from p-Alkoxypropionates. Spectacular progress in the 1970s led to the rapid development of organotransition-metal chemistry, particularly to catalyze olefin reactions (93,94). A number of patents have been issued (28,95—97) for the oxidative carbonylation of ethylene to provide acryUc acid and esters. The procedure is based on the palladium catalyzed carbonylation of ethylene in the Hquid phase at temperatures of 50—200°C. Esters are formed when alcohols are included. Anhydrous conditions are desirable to minimize the formation of by-products including acetaldehyde and carbon dioxide (see Acetaldehyde). 

Acetates. Anhydrous iron(II) acetate [3094-87-9J, Ee(C2H202)2, can be prepared by dissolving iron scraps or turnings in anhydrous acetic acid ( 2% acetic anhydride) under an inert atmosphere. It is a colorless compound that can be recrystaUized from water to afford hydrated species. Iron(II) acetate is used in the preparation of dark shades of inks (qv) and dyes and is used as a mordant in dyeing (see Dyes and dye intermediates). An iron acetate salt [2140-52-5] that is a mixture of indefinite proportions of iron(II) and iron(III) can be obtained by concentration of the black Hquors obtained by dissolution of scrap iron in acetic acid. It is used as a catalyst of acetylation and carbonylation reactions. 

The vast majority of commercial apphcations of methacryhc acid and its esters stem from their facile free-radical polymerizabiUty (see Initiators, FREE-RADICAl). Solution, suspension, emulsion, and bulk polymerizations have been used to advantage. Although of much less commercial importance, anionic polymerizations of methacrylates have also been extensively studied. Strictiy anhydrous reaction conditions at low temperatures are required to yield high molecular weight polymers in anionic polymerization. Side reactions of the propagating anion at the ester carbonyl are difficult to avoid and lead to polymer branching and inactivation (38—44). 

A related but distinct rhodium-catalyzed methyl acetate carbonylation to acetic anhydride (134) was commercialized by Eastman in 1983. Anhydrous conditions necessary to the Eastman acetic anhydride process require important modifications (24) to the process, including introduction of hydrogen to maintain the active [Rhl2(CO)2] catalyst and addition of lithium cation to activate the alkyl methyl group of methyl acetate toward nucleophilic attack by iodide. 

Unlike simple, unhindered carbonyl compounds, the quinones do not yield bisulfite addition products, but undergo ring addition. Another significant carbonyl reaction is the addition of tertiary phosphites under anhydrous conditions (98). The ester product (99) is easily hydroly2ed, and the overall sequence produces excellent yields of hydroquinone monoethers. 

The zirconium—nitrogen bond is weaker than the zirconium—oxygen bond even under anhydrous conditions. When zirconium tetrachloride reacts with carbonyl-containing amides such as... 

Low Oxidation State Chromium Compounds. Cr(0) compounds are TT-bonded complexes that require electron-rich donor species such as CO and C H to stabilize the low oxidation state. A direct synthesis of Cr(CO)g, from the metal and CO, is not possible. Normally, the preparation requires an anhydrous Cr(III) salt, a reducing agent, an arene compound, carbon monoxide that may or may not be under high pressure, and an inert atmosphere (see Carbonyls). 

The protonated azirine system has also been utilized for the synthesis of heterocyclic compounds (67JA44S6). Thus, treatment of (199) with anhydrous perchloric acid and acetone or acetonitrile gave the oxazolinium perchlorate (207) and the imidazolinium perchlorate (209), respectively. The mechanism of these reactions involves 1,3-bond cleavage of the protonated azirine and reaction with the carbonyl group (or nitrile) to produce a resonance-stabilized carbonium-oxonium ion (or carbonium-nitrilium ion), followed by attack of the nitrogen unshared pair jf electrons to complete the cyclization. 

Cyclic g-haloacetals and -ketals have been prepared by variations on two basic methods. The most frequently used method involves the combination of an a,B-unsaturated carbonyl compound (acrolein, methyl vinyl ketone, croton-aldehyde, etc.) a diol, and the anhydrous hydrogen halide. All possible sequences of combining these three have been used. In most cases the... 

Complete exchange of protons in a sterically unhindered position a to a carbonyl group can be achieved by heating a solution of the ketone in O-deuterated solvents in the presence of an acid or base catalyst, the latter being the more effective. The most commonly used solvents are methanol-OD, ethanol-OD, and the aprotic solvent anhydrous tetrahydrofuran or dioxane mixed with deuterium oxide. Under alkaline conditions the exchange rate in 153 2 14,164 stcroids, for example, is usually... 

The total yield of products from alkanecarboxyhc acids increases, in most cases, by addition of anhydrous hydrogen fluoride. The optimum hydrogen fluoride concentration is much higher than catalytic and is related to the basicity of a carbonyl group. A mechanism for the formation of both 1,1,1-trifluoroalkanes and bis(l,l-difluoroalkyl) ethers has been proposed [206] (equation 102)... 

Enamines derived from aldehydes can usually be obtained by the reaction of 2 equivalents of a secondary amine with the carbonyl compound, in the presence of anhydrous potassium carbonate, followed by pyrolytic distillation of the aminal with elimination of one of the amine groups (10,15, 30-36). Ketones are directly converted to enamines under the conditions of aminal formation. The azeotropic removal of water with excess aldehyde has also been described (32,37). 

A methyl group in the 2-position of the selenazole ring shows the same reactivity as the analogous thiazoles toward carbonyl compounds. By reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride catalyst, 4-methyl-2-styryl-selcnazole (9), mp 74-75°C, could be prepared. ... 

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