Ketenes acetyl

Four different methods (vapour-phase acetylation using acetic anhydride, acetylation using ketene gas, liquid phase acetylation using acetic anhydride/xylene, or neat acetic anhydride) were used to acetylate pine wood chips to a variety of WPGs for the production of MUF-bonded particleboards (Nilsson etal., 1988). Composite boards were exposed to unsterile soil in fungal cellar tests. Boards made from ketene acetylated chips were not found to be resistant to decay at the maximum WPG level achieved (17 %) with a liquid acetic anhydride modification, no decay was recorded at a WPG level of c. 18 % after 12 months exposure, whereas with a vapour-phase treatment at the same WPG, evidence for decay was found. 

Ketals, of hexitols, IV, 223 Ketene, acetylation of starch with, I, 290 Keto acids, a- and 0-, specificity of carboxylase action on, V, 50 a-Keto acids, aromatic, V, 50 0-Keto acids, oxidation of, II, 148 a-Ketobutyric acid, V, 50 a-Ketocaproio acids, V, 50 Ketogenesis, in liver slices, II, 155 Ketolysis, II, 120, 146, 147, 158 in liver slices, II, 155 Ketolytic, II, 146... 

Isopropenyl acetate, obtained from ketene and acetone, reacts as an activated ester of acetic acid and, like its generator ketene, acetylates amides highly exothermally at room temperature.784 Even 1-acetylimidazole, which is difficult to prepare in other ways, is thus obtained from imidazole in 94% yield.785... 

TMAL) reaction sequence for the synthesis of P-lactones. Despite the relatively high diastereoselectivity, the ZnCb mediated aldol reaction was only optimized when smaller silyl and thiol groups of the ketene acetyl were employed for the improved efficiency of the subsequent lactonization. The methodology was utilized in the synthesis of (-)-panicilin D, a pancreatic lipase inhibitor, where the ketene thioacetal 60 was added to aldehyde 59, upon which lactonization followed by deprotection yielded the 3-lactone 61 as a diastereomeric mixture (9.3 1) in modest yield. 

Acetic acid, HCL, and traces of CO2, ketene, acetyl chloride, CO andCH4... 

The Hydrate and Enol Form. In aqueous solutions, acetaldehyde exists in equihbrium with the acetaldehyde hydrate [4433-56-17, (CH2CH(0H)2). The degree of hydration can be computed from an equation derived by BeU and Clunie (31). Hydration, the mean heat of which is —21.34 kJ/mol (—89.29 kcal/mol), has been attributed to hyperconjugation (32). The enol form, vinyl alcohol [557-75-5] (CH2=CHOH) exists in equihbrium with acetaldehyde to the extent of approximately 1 molecule per 30,000. Acetaldehyde enol has been acetylated with ketene [463-51-4] to form vinyl acetate [108-05-4] (33). 

Chloroacetyl chloride is manufactured by reaction of chloroacetic acid with chlorinating agents such as phosphoms oxychloride, phosphoms trichloride, sulfuryl chloride, or phosgene (42—44). Various catalysts have been used to promote the reaction. Chloroacetyl chloride is also produced by chlorination of acetyl chloride (45—47), the oxidation of 1,1-dichloroethene (48,49), and the addition of chlorine to ketene (50,51). Dichloroacetyl and trichloroacetyl chloride are produced by oxidation of trichloroethylene or tetrachloroethylene, respectively. 

DimeriZa.tlon. A special case of the [2 + 2] cyclo additions is the dimerization of ketenes. Of the six possible isomeric stmctures, only the 1,3-cyclobutanediones and the 2-oxetanones (P-lactones) are usually formed. Ketene itself gives predominandy (80—90%) the lactone dimer, 4-methylene-2-oxetanone (3), called diketene [674-82-8], approximately 5% is converted to the symmetrical dimer, 1,3-cyclobutanedione [15506-53-3] (4) which undergoes enol-acetylation to so-called triketene [38425-52-4] (5) (44). 

The manufacture of the highly pure ketene required for ketenization and acetylation reactions is based on the pyrolysis of diketene, a method which has been employed in industrial manufacture. Conversion of diketene to monomeric ketene is accompHshed on an industrial scale by passing diketene vapor through a tube heated to 350—600°C. Thus, a convenient and technically feasible process for producing ketene uncontaminated by methane, other hydrocarbons, and carbon oxides, is available. Based on the feasibiHty of this process, diketene can be considered a more stable form of the unstable ketene. 

Uses. The lowest member of this class, ketene itself, is a powerful acetylating agent, reacting with compounds containing a labile hydrogen atom to give acetyl derivatives. This reaction is used only when the standard acetylation methods with acetic anhydride or acetyl chloride [75-36-5] do not work weU. Most of the ketene produced worldwide is used in the production of acetic anhydride. Acetic anhydride is prepared from the reaction of ketene and acetic acid. 

Ketones with labile hydrogen atoms undergo enol acetylation on reaction with ketene. Strong acid catalysis is required. If acetone is used, isoptopenyl acetate [108-22-5] (10) is formed (82—85). Isopropenyl acetate is the starting material for the production of 2,4-pentanedione (acetylacetone) [123-54-6] (11). 

Ketene has also been used on a large scale for C-acetylation in the synthesis of the carbapenem antibiotic thienamycin [59995-64-1] (86,87). 

Acylation. Reaction conditions employed to acylate an aminophenol (using acetic anhydride in alkaU or pyridine, acetyl chloride and pyridine in toluene, or ketene in ethanol) usually lead to involvement of the amino function. If an excess of reagent is used, however, especially with 2-aminophenol, 0,A/-diacylated products are formed. Aminophenol carboxylates (0-acylated aminophenols) normally are prepared by the reduction of the corresponding nitrophenyl carboxylates, which is of particular importance with the 4-aminophenol derivatives. A migration of the acyl group from the O to the N position is known to occur for some 2- and 4-aminophenol acylated products. Whereas ethyl 4-aminophenyl carbonate is relatively stable in dilute acid, the 2-derivative has been shown to rearrange slowly to give ethyl 2-hydroxyphenyl carbamate [35580-89-3] (26). 

Production is by the acetylation of 4-aminophenol. This can be achieved with acetic acid and acetic anhydride at 80°C (191), with acetic acid anhydride in pyridine at 100°C (192), with acetyl chloride and pyridine in toluene at 60°C (193), or by the action of ketene in alcohoHc suspension. 4-Hydroxyacetanihde also may be synthesized directiy from 4-nitrophenol The available reduction—acetylation systems include tin with acetic acid, hydrogenation over Pd—C in acetic anhydride, and hydrogenation over platinum in acetic acid (194,195). Other routes include rearrangement of 4-hydroxyacetophenone hydrazone with sodium nitrite in sulfuric acid and the electrolytic hydroxylation of acetanilide [103-84-4] (196). 

Carbonyl Compounds. Cychc ketals and acetals (dioxolanes) are produced from reaction of propylene oxide with ketones and aldehydes, respectively. Suitable catalysts iaclude stannic chloride, quaternary ammonium salts, glycol sulphites, and molybdenum acetyl acetonate or naphthenate (89—91). Lactones come from Ph4Sbl-cataly2ed reaction with ketenes (92). 

Various processes involve acetic acid or hydrocarbons as solvents for either acetylation or washing. Normal operation involves the recovery or recycle of acetic acid, any solvent, and the mother Hquor. Other methods of preparing aspirin, which are not of commercial significance, involve acetyl chloride and saHcyHc acid, saHcyHc acid and acetic anhydride with sulfuric acid as the catalyst, reaction of saHcyHc acid and ketene, and the reaction of sodium saHcylate with acetyl chloride or acetic anhydride. 

Ketene is an efficient acetylating agent with some alcohols, but in the absence of catalysts may be either nonieactive or sluggish with others, especially phenols and tertiary alcohols (72) (see Ketbnes AND RELATBD substances). 

Although acetyl chloride and ketene (CH2 = C = O) have been described in the literature, acetic anhydride has been the commonly employed acetylating agent. 

Sulfur tnoxide adds to 2,2 difluoroethylenesulfonyl fluoride to afford the P sultone and its rearrangement product, bis(fluorosulfonyl)acetyl fluoride Potassium fluoride acts as a base and reacts with the acetyl fluoride to eliminate the elements of hydrogen fluoride and produce bis(fluorosulfonyl)ketene [IS] (equation 6)... 

Bis(tnfluoromethyl)-4,5-dihydrooxazin-6-ones [28] and their O-acetylated dcnvatives [96] are formed on treatment of acyl imines with acetyl chloride-hiethylamine at room temperature. The reaction was interpreted as a cycloaddition reaction involving a ketene [28] However, the periselectivity and regiochemistry of this reactwn-are not in agreement with results obtained from the reaction of... 

Dehydrochlorination of bis(tnfluoromethylthio)acetyl chloride with calcium oxide gives bis(trifluoromethylthio)ketene [5] (equation 6) Elimination of hydrogen chloride or hydrogen bromide by means of tetrabutylammonium or potassium fluoride from vinylic chlorides or bromides leads to acetylenes or allenes [6 (equation 7) Addition of dicyclohexyl-18-crown-6 ether raises the yields of potassium fluoride-promoted elimination of hydrogen bromide from (Z)-P-bromo-p-ni-trostyrene in acetonitrile from 0 to 53-71 % In dimethyl formamide, yields increase from 28-35% to 58-68%... 

The reaction of ketene with the enamine (113) is reported (88) to give l-morpholino-2-acetyl-l-cyclohexene i.e., the enamino ketone expected from acylation of (113). The pyrrolidine enamine (28), however, has been shown to react (73) with excess ketene to give the a-pyrone (124). On the... 

Reaction of 3-(4-methylphenylamino)-4-(4-methylphenylimino)-4//-pyr-ido[l,2-a]pyrazine (373, R = 4-MePh) with ketenes 393, prepared in situ from the appropriate acetyl chloride with NEt3, yielded tricyclic derivatives... 

The filtrate from this first batch will comprise a solution of 180 to 270 kg of unprecipitated acetylsalicylic acid (1.0 to 1.5 mols), 510 kg of acetic anhydrice (5.0 mols), 600 kg of acetic acid (10.0 mols) (obtained as a by-product in the acetylation step) and 1,200 kg of the diluent toluene. Into this filtrate, at a temperature of 15° to 25°C, ketene gas is now passed through a sparger tube or diffuser plate, with good agitation, until a weight increase of 420.5 kg of ketene (10 mols) occurs. The reaction mixture wiil now contain 180-270 kg of unprecipitated acetylsalicylic acid (1.0-1.5 mols) and 1,532 kg of acetic anhydride (15 mols) in 1,200 kg of toluene. This mother liquor is recycled to the first step of the process for reaction with another batch of 1,382 kg of salicylic acid. On recirculating the mother liquor, the yield of pure acetylsalicylic acid is 1,780 to 1,795 kg per batch. 

After filtration of the reaction mixture, treatment of the toluene filtrate with ketene gas accomplishes a smooth mono-C-acetylation of the nucleophilic enamine function in 25, and provides keto enamine... 

Schemes 28 and 29 illustrate Curran s synthesis of ( )-hirsutene [( )-1]. Luche reduction58 of 2-methylcyclopentenone (137), followed by acetylation of the resulting allylic alcohol, furnishes allylic acetate 138. Although only one allylic acetate stereoisomer is illustrated in Scheme 28, compound 138 is, of course, produced in racemic form. By way of the powerful Ireland ester enolate Clai-sen rearrangement,59 compound 138 can be transformed to y,S-unsaturated tm-butyldimethylsilyl ester 140 via the silyl ketene acetal intermediate 139. In 140, the silyl ester function and the methyl-substituted ring double bond occupy neighboring regions of space, a circumstance that favors a phenylselenolactonization reac-...

Acetyl-l//-azepine (20%) is formed by A-acetylation of 1//-azcpine with ketene.9... 

Acetates (loss of ketene, see if m/z 43 is also present) (V-acetylated compounds (acetamides)... 

There are many methods for the preparation of ethane-1-hydroxy-1,1-diphosphonic acid including reacting phosphorus trichloride and acetic acid in the presence of tributylamine [106], phosphorus with acetic acid and oxygen [108], acetic anhydride with phosphorous acid and acetyl chloride [80,84-86,109,110], and acetic anhydride with phosphoric acid and acetic acid [111]. By another method ketene and phosphorous acid can be used [112], as shown in Eq. (68) ... 

Following a similar strategy, trifluoro acetyl ketene diethyl acetal was successively condensed with 2-aminothiophenol in the presence of toluene in a multimode microwave oven (8 min at 980 W) to give the 2-(l,l,l-trifluoro-acetonyl)benzothiazole ring in an excellent yield (93%) [14] (Scheme 13). hi this work, the temperature reached during reaction was not controlled reducing the reproducibility of the process. 

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