Esters, Lactones, and Acid Anhydrides

The equilibrium concentrations of esters may become higher with increasing temperatures. Usually for the hydrogen pressures above 21 MPa and temperatures below 260°C, the concentration of esters at equilibrium is very small and practically not important. As the most favorable conditions for the reaction at 250°C, Adkins recommends an initial hydrogen pressure of 24 MPa, the maximum pressure of 41 MPa at the temperature of reaction, and 21 MPa or higher at completion.32 Typical hydrogenations of esters of mono- and dicarboxylic acids are given in eqs. 10.735 and 10.8,36 respectively. 

The tendency toward hydrogenolysis to give hydrocarbons is greatly reduced with phenylacetic esters where a homobenzyl-type alcohol is produced. If the hydrogenation was stopped before the absorption of hydrogen was complete, a 39.7% yield of 2-phenethyl alcohol was obtained over Cu-Ba-Cr oxide even at 250°C. The yield was further increased to 58.3% over Cu-Mg-Cr oxide (eq. 10.20), and the yields from the cyclohexyl ester was 58.7% over Cu-Ba-Cr oxide and 63.3% over Cu-Ca-Cr oxide. In contrast, over a catalyst containing no alkaline-earth metal oxide, the predominant product from the ethyl ester became ethylbenzene (88.7%), and 2-phenethyl alcohol was obtained in only 4.5% yield. 

Further, in the case of ethyl 3-phenylpropionate with two CH2 groups between the phenyl and the ester groups, the yield of the corresponding alcohol became almost quantitative over Cu-Ba-Cr oxide at 250°C (eq. 10.21).35 

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It includes alcohols, esters, lactones and acid anhydrides. 

Carbohydrates and glycosides Aldehydes, ketones and related con unds Quinones Carboxylic acids Phenols and enols Esters, lactones and acid anhydrides of carboxylic acids Alcohols Ethers Hydrocarbons... 

The reaction under consideration is typified by the formation of saturated carboxylic acids from olefins, carbon monoxide, and water. Other compounds have been used in place of olefins (alkyl halides, alcohols), and besides water, a variety of compounds containing active hydrogen may be employed. Thus, alcohols, thiols, amines, and acids give rise to esters, thio-esters, amides, and acid anhydrides, respectively (15). If the olefin and the active hydrogen are part of the same molecule, three or four atoms apart, cyclizations may occur to produce lactones, lactams, imides, etc. The cyclizations are formally equivalent to carbonylations, however, and will be considered later. 

In summary, the reactivity of various functional groups toward Li 9-BBNH is classified into four broad categories [18] (1) rapid- or fast-reduction aldehyde, ketone, ester, lactone, acylchloride, acid anhydride, epoxide, disulfide, -alkyli-odide, and tosylate (2) slow-reduction tertiary amide, alkylbromide, and aromatic nitrile (3) sluggish-reduction carboxylic acid, aliphatic nitrile, primary amide, nitro and azoxy compounds, and secondary alkylbromide and tosylate (4) inert olefin, oxime, alkylchloride, sulfoxide, azo-compound, sulfide, sulfone, and sulfonic acid. 

Since the discovery of the synthesis of 1,3,5-triazine-2,4-diamines from biguanide and its derivatives,328-329 a large variety of carboxylic acid derivatives, e.g. acid chlorides,332 342,346 lactones,333 amides,334,335 imides,336,337 ortho esters,338 amidines,338 esters334, 339- 343 and acid anhydrides,332,344,345 have been used as starting materials in the preparation of these triazines (Table 8).330,331 The preferred procedure is the reaction of biguanides 1 with esters 2 in alcoholic solution, sometimes in the presence of a basic catalyst. The reaction mechanism is thought to be as indicated.341... 

Lithium aluminum hydride (LiAlH4) is the most powerful of the hydride reagents. It reduces acid chlorides, esters, lactones, acids, anhydrides, aldehydes, ketones and epoxides to alcohols amides, nitriles, imines and oximes to amines primary and secondary alkyl halides and toluenesulfonates to... 

Acids, Esters, Lactones, Amides, Imides, and Anhydrides... 

In summary, reactions of nitronates with acid anhydrides or acyl chlorides give the O-acylated products, and reactions with acyl imidazoles, phenyl esters, acyl nitriles, and enol-lactones gives the C-acylated products, (see Eq. 5.13).25 The C/O selectivity of nitronate acylation by RCOX is qualitatively correlated with strength (pKJ of the acid HX conjugated to the leaving group X .25... 

In this short section, cyclic compounds are discussed that are not strictly lactones since they contain an endocyclic structural motif of the type -O-CO-X- or -X-O-CO-. However, these compounds share with lactones the possibility to be hydrolyzed at the endocyclic -CO-O- bond. This is the case for cyclic diesters of carbonic acid (-O-CO-O-), cyclic esters of car-bamic acid (-0-C0-NH-), and cyclic anhydrides (-C0-0-C0-). One example of each class is presented here. 

Copolymerizations between pairs of cyclic esters, acetals, sulfides, siloxanes, alkenes, lactams, lactones, /V-carboxy-a-amino acid anhydrides, imines, and other cyclic monomers... 

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