Benzene acetoxylation

Scheme 8.14 Pd-catalyzed aerobic benzene acetoxylation and nitration in the presence of NO, [51, 54].

The kinetics of nitration in acetic anhydride are complicated. In addition to the initial reaction between nitric acid and the solvent, subsequent reactions occur which lead ultimately to the formation of tetranitromethane furthermore, the observation that acetoxylation accompanies the nitration of the homologues of benzene adds to this complexity. 

Acetoxylation and nitration. It has already been mentioned that 0- and m-xylene are acetoxylated as well as nitrated by solutions of acetyl nitrate in acetic anhydride. This occurs with some other homologues of benzene, and with methyl phenethyl ether,ii but not with anisole, mesitylene or naphthalene. Results are given in table 5.4. 

The addition of sulphuric acid increased the rate of nitration of benzene, and under the influence of this additive the rate became proportional to the first powers of the concentrations of aromatic, acetyl nitrate and sulphuric acid. Sulphuric acid markedly catalysed the zeroth-order nitration and acetoxylation of o-xylene without affecting the kinetic form of the reaction. ... 

TABLE 5.4 Yields moles %) in the nitration and acetoxylation of some derivatives of benzene at 25 °C... 

Three oxidative reactions of benzene with Pd(OAc)2 via reactive rr-aryl-Pd complexes are known. The insertion of alkenes and elimination afford arylalk-enes. The oxidative functionalization of alkenes with aromatics is treated in Section 2.8. Two other reactions, oxidative homocoupling[324,325] and the acetoxylation[326], are treated in this section. The palladation of aromatic compounds is possible only with Pd(OAc)2. No reaction takes place with PdCl2. 

A direct method for introduction of a C-21 acetoxyl group into a 20-keto-pregnane is by reaction with lead tetraacetate at room temperature. Although originally the reaction carried out in hot acetic acid gave low yields, a careful study by Henbest has defined conditions so that yields as high as 86 % can be obtained at room temperature. The preferred solvent is 5 % methanol in benzene, with boron trifluoride etherate as catalyst. With either methanol or benzene, the yield is less than 4%. 

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

Alkyl groups on triazole have similar properties to those on benzene and can be oxidised in a similar way. Derived functions such as CH2OH and CH2Br behave in the expected manner. The acetoxylation of (86) with acetic anhydride to give (87) is unexpected (Equation (31)) <70JPR610>. 

Highly selective formation of phenyl acetate was observed in the oxidation of benzene with palladium promoted by heteropoly acids.694 Lead tatraacetate, in contrast, usually produces acetoxylated aromatics in low yields due to side reac-tions. Electrochemical acetoxylation of benzene and its derivatives and alkoxylation of polycyclic aromatics789 790 are also possible. Thermal or photochemical decomposition of diacyl peroxides, when carried out in the presence of polycyclic aromatic compounds, results in ring acyloxylation.688 The less reactive... 

The effects of added species. The rate of nitration of benzene, according to a rate law kinetically of the first order in the concentration of aromatic, was reduced by sodium nitrate, a concentration of io 3 mol l-1 of the latter retarding nitration by a factor of about 4.llc>28 Lithium nitrate anticatalysed the nitration and acetoxylation of o-xylene in solutions of acetyl nitrate in acetic anhydride. The presence of 6 x io-4 mol 1 1 of nitrate reduced the rate by a factor of 4, and modified the kinetic form of the nitration from a zeroth-order dependence on the concentration of aromatic towards a first-order dependence. However, the ratio of acetoxylation to nitration remained constant.146 Small concentrations of sodium nitrate similarly depressed the rate of nitration of anisole and again modified the reaction away from zeroth to first-order dependence on the concentration of the aromatic.116... 

These and related reactions of lead tetraacetate have been widely used in synthetic organic chemistry, and are the subject of several reviews.6-10 However, they have found relatively few applications in the carbohydrate field specifically. One important application has been the synthesis of ketones by way of acetoxylation of suitable unsaturated compounds. By treating 1,2-0-isopropylidene-2-propene-l, 2-diol (I) in benzene at 50° with... 

Acetoxylation of thiochroman-4-one can be accomplished in excellent yield using Mn(OAc)3 in a mixed benzene-acetic acid solvent (Equation 54) <2004T3427>. 

Arpe and Hornig595 carried out a thorough investigation of palladium-catalyzed acetoxylation of benzene in acetic acid. Selectivities as high as 78% were observed with a heterogeneous Pd/Au-on-Si02 catalyst at 155°C. 

Reacticm of ketcmes with LTA in benzene in the presence of boron trifluoride etherate at or below room temperature effects rapid a-acetoxylation." The yields are indeed improved in most cases, for... 

Preformed enolates are susceptible to further methods of oxygenation. For example treatment with LTA in benzene effects a-acetoxylation at lower temperature and more rapidly than the corresponding enol examples. Similarly a-benzoylation using benzoyl peroxide is possible for both lactones and 3-keto esters and presumably could be used for less-activated ketones. 

Favorski-type rearrangement Reaction of lead tetraacetate and BFj in benzene with the ketone (1) results in a mixture of a -acetoxylated ketones, 2a and 2b. If... 

Catechol to phenol rearrangement. Treatment of 2-acetoxy-4-(methylthio)-3,5-xylenol (1) with triethylamine (benzene, reflux) leads to 2, also obtained from 3 under the same conditions. This migration of an acetoxyl group is probably related to the Pummerer rearrangement. ... 

ACETOXYL see BDSOOO p-(ACETOXYMERCURI)ANILINE see ABQOOO (ACETOXYMERCURI)BENZENE see ABU500 2-(ACETOXYMERCURI)-4-NITROANIUNE see ABQ250... 

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