Acetic acid diketene

Boiling acetic acid converts 2-aminothiazole into the 2-acetamido derivative far more easily when catalytic amounts of diketene are added to the reaction mixture (277),... 

Anhydride manufactured by acetic acid pyrolysis sometimes contains ketene polymers, eg, acetylacetone, diketene, dehydroacetic acid, and particulate carbon, or soot, is occasionally encountered. Polymers of aHene, or its equilibrium mixture, methylacetylene—aHene, are reactive and refractory impurities, which if exposed to air, slowly autoxidize to dangerous peroxidic compounds. 

For the two most important industrial uses, the gaseous ketene is immediately treated with acetic acid to form acetic anhydride or dimerized to diketene. 

The reaction may proceed in water, acetic acid, or any other organic solvent or mixture that is inert to diketene. This group also includes bifunctional coupling components of the bisacetoacetic diaminodiphenyl type ... 

Since reaction of wood with acetic anhydride leads to the formation of acetic acid by-product, which must be removed from the wood, there has been some interest in the use of ketene gas for acetylation (Figure 4.4a). Ketene, for reaction with wood, is produced by pyrolysis of diketene. Provided that the wood contains no moisture, no acetic acid by-product is produced. However, ketene presents handling problems it is very toxic and explosive, and it also has a tendency to dimerize. A comprehensive series of studies of ketene-based acetylation has been performed in Latvia and this work has been reviewed by Morozovs etal. (2003). Hardwoods have been found to be more reactive to ketene than softwoods and the optimal temperature for reaction has been determined as 47 °C. Application of vacuum and treatment of wood with ammonia solution has been used to remove the excess ketene. The reaction of wood with liquid diketene was also studied, with a WPG of 35 % being obtained after reaction for 3 hours at 52 °C. 

Methyluracils 947 are readily prepared by reaction of ureas with diketene 945 in acetic acid, and although mixtures of products are obtained with substituted ureas, this procedure has been used synthetically to prepare a variety of 1-substituted and 1,3-disubstituted 6-methyluracils, using both solution- and solid-phase procedures <2000TL1487, 2003CPB1025, 2004JME1259>. 

A similar type of acid-catalyzed condensation of aldehydes with 4-methylene-2-oxetanone (diketene), giving 4-oxo-6-methyl-l,3-dioxins, has been patented (73GEP2149650). However, other work has established that <5-hydroxy-/3-keto acids or unsaturated keto acids are formed as the principal products (equation 24) (78CPB3877, 78CL409). The latter reaction probably involves electrophilic attack of the protonated aldehyde on the nucleophilic exocyclic methylene carbon atom of the diketone. A closely related reaction of acetals with diketene, catalyzed by titanium tetrachloride, gives the corresponding <5-alkoxy-/3-keto esters (74CL1189). 

They also described the reaction of diketene with N,N-dimethylurea in acetic acid, yielding 50 (see also Ahmed et a/.177). Gunar et a/.178 used diketene in the reaction with cyanic acid (see also Ozaki179), thiocyanic acid, ethyl urethane, and N,N -disubstituted ureas in acetic acid medium to obtain 50. When a 2-thiono derivative was obtained from thiocyanic acid, as in Eq. (37), they desulfurized it with mercuric acetate. 

Six-Membered Heterocycle Ring Formation. Heterocycle formation involving diketene usually involves acetoacetylation of a substrate, followed by intramolecular condensation. Diketene itself readily dimerizes through self-condensation forming mainly dehydro acetic acid [771-03-9] (DHA) (13). Dehydroacetic acid and sodium dehydro acetate [4418-26-2] are used as preservatives for foods and cosmetics. DHA is found as an unwanted by-product in many diketene reactions, but can be obtained intentionally by dimerizing diketene in the presence of pyridine [110-86-1] in benzene, diazabicyclo[2.2.2]octane [280-57-9] (DABCO), and other basic catalysts. 

Presence of mineral or Lewis acids, or bases including amines, will catalyse violent polymerisation of this very reactive dimer, accompanied by gas evolution [1], Sodium acetate is sufficiently basic to cause violent polymerisation at 0.1% concentration when added to diketene at 60°C [2]. A Russian paper describing a tank rupture incident triggered by ingress of acetic acid and pyridine, with suggested precautions against recurrence, is abstracted [3]. 

Dehydration of primary nitroalkanes with phenyl isocyanate or acetic anhydride in the presence of catalytic triethylamine affords nitrile oxides, which may be trapped as their 1,3-dipolar cycloadducts or allowed to dimerize to the corresponding furoxans. Other dehydrating agents that have been used include diketene, sulfuric acid and, when the a-methylene group is activated by electron-withdrawing groups, boron trifluoride in acetic anhydride, trifluoroacetic anhydride with triethylamine, and nitric acid in acetic acid. 

The action of a Zn/Cu couple on 1,3-dibromo ketones and secondary amides yields 2-dialkylamino-1,3-dioxolanes (451 equation 208). Fluorosulfonic peracid anhydride adds to trifluoroacetonitrile to give an amide acetal (452 equation 209). In the addition of (Z)-2-butene-l,4-diol to trichloroacetoni-trile, catalyzed by sodium, the 1,3-dioxepin (453 equation 210) is produced. Bicyclic amide acetals (454 equation 211) are byproducts in the reaction of lactim ethers with diketene. TTie methyl esters of perfluorinated carboxylic acids react with diethanolamine to afford bicyclic amide acetals (455 equation 212). Heating of maleic anilides (456 equation 213) with acetic acid anhydride/sodium acetate gives heterocyclic compounds (457) containing an amide acetal structure. ... 

The second conversion, which is exothermic, can be carried out in the absence of catalyst, by absorption in acetic acid, between 30 and 40 C at reduced pressure (7 to 20 kPa). Higher temperatures and pressures facilitate the dimerization of ketene to diketene, whose major drawback is to have a boiling point (bpYon = 127.4°C) fairly close to that of th anhydride. Less than 2 per cent weight is usually formed, so that the yield of the operation., with respect to both the acid and ketene. is higher than 95 to 98 molar per cent. 

Good yields of 5-oxo-l,3-oxazines (212) have been obtained by treatment of the diazo-ketones (211) with strong acid. The reaction of jV-alkyl-cyanamides (RNHCN) with diketen gives oxazin-4-ones (213), which may be transformed into uracils (214) by refluxing in acetic acid. ... 

Sugasawa et al.u in a series of model studies directed toward the total synthesis of camptothecin, allowed 2-pyrrolidinone (53) to react with diketene (54) followed by ammonium acetate in acetic acid to afford 2-methyl-4,6,7,8-tetrahydropyrrolo[l,2-a]pyrimidin-4-one (56). Presumably, keto imide 55 is an intermediate in this reaction [Eq. (15)]. 

EXPLOSION and FIRE CONCERNS extremely flammable gas gas is heavier than air and may travel along the ground distant ignition possible forms explosive gas/air mixtures substance may readily polymerize reacts with water to form acetic acid violent reaction with many organic compounds NFPA rating (not rated) rapidly forms explosive diacetyl peroxide upon interaction with hydrogen peroxide dimerizes to diketene even at low temperatures toxic gases and vapors, such as carbon monoxide, may be released in a fire use dry powder or carbon... 

Diketene (4-methyleneoxetane-2-one) is formed by dimerization of ketene which in turn is prepared by pyrolysis of acetone or acetic acid. The compound is an industrial intermediate. It ring-opens with ethanol to give ethyl acetoacetate the nucleophile attacks the C-atom of the carbonyl group. 

The reaction of diketene in dilute acetic acid with aniline yields acetoacetanilide from which azo pigments such as Kgment Yellow 1 are derived. An important azo dye based on this raw material is Acid Yellow 151. (Likewise, homologs of aniline (e.g. xylidines) are used for the production of acetoacetanilide pigments such as Pigment Yellow 13.)... 

Thioamides react with diketene in acetic acid or xylene 6-substituted-4-hydroxy-2-pyridones (Xn-lOS). form... 

The sixth item in Table 9.6 illustrates the reaction between ketene (CH2=C=0) and ethanoic acid (acetic acid,CH3C02H). As shown in Equation 9.99,ketene (CH2=C=0) can be prepared by the dehydration of ethanoic acid (acetic acid, CH3CO2H), and the isolation of ketene is complicated because of its ready dimerization to diketene (4-methylideneoxacyclobutane-2-one). 

---