Schotten-Baumann method

In the Schotten-Baumann method of benzoylation, the hydroxyl- or amino-compound (or a salt of the latter) is dissolved or suspended in an excess of 10% aqueous sodium hydroxide solution, a small excess (about 10% more than the theoretical amount) of benzoyl chloride is then added and the mixture vigorously shaken. Benzoylation proceeds smoothly under these conditions, and the solid benzoyl compound, being insoluble in water, separates out. The sodium hydroxide then hydrolyses the excess of benzoyl chloride, giving sodium... 

The dibenzoyl derivatives can be prepared by the normal Schotten-Baumann method, using 10% aqueous sodium hydroxide and an excess of benzoyl chloride, but the m.ps. of the dibenzoyl derivatives are inconveniently high (p- ssO-... 

The Schotten - Baumann method of benzoylation with benzoyl chloride in the presence of aqueous sodium hydroxide may be used. Full details are given under Amines Section IV.lOO, 2. 

It must further be mentioned that the acylation of alcohols, phenols, and amines with acid chlorides (and also anhydrides) is now frequently carried out in pyridine solution instead of according to the older Schotten-Baumann method (action of acid chloride in aqueous-alkaline suspension). The hydrogen chloride is fixed by the pyridine. 

These benzoyl derivatives were prepared by shaking the amino acid with excess of benzoyl chloride in the presence of sodium bicarbonate instead of in the presence of excess of alkali, i.e., by the Schotten-Baumann method, which gave poor and varying yields of the benzoyl compound. 

The Schotten-Baumann method of benzoylation with benzoyl chloride in the presence of aqueous sodium hydroxide may be used. Full details are given under Primary and secondary amines, Section 9.6.21, p. 1273. Alternatively, dissolve 1.0 g of the phenol in 3 ml of dry pyridine and add 0.5 g of benzoyl chloride. After the initial reaction has subsided, warm the mixture over a small flame for a minute or two and pour, with vigorous stirring, into 10-15 ml of water. Allow the precipitate to settle, decant the supernatant liquid, stir the residue thoroughly with 5-10 ml of m sodium carbonate solution, filter and recrystallise from ethanol or from light petroleum. 

Jursic, B. S., Neumann, D. Preparation of N-acyl derivatives of amino acids from acyl chlorides and amino acids in the presence of cationic surfactants. A variation of the Schotten-Baumann method of benzoylation of amino acids. Synth. Common. 2001, 31, 555-564. 

The two Schotten-Baumann methods of preparing diacyl peroxides suffer from the formation of difficult emulsions in the alkaline medium and loss in yield due to hydrolysis of the acid chloride. Silbert and Swern developed an improved method involving acylation of 50-65% hydrogen peroxide with the acid chloride in ethei pyridine solution and obtained highly pure diacyl peroxides in nearly quantitative yield. For example, a solution of myristoyl chloride in ether is cooled to 0°. hydrogen... 

The Schotten-Baumann method can also be applied with acetyl chloride, but because of the sensitivity of this chloride it is better replaced by some other process, e.g., use of acetic anhydride. 

A procedure due to Einhorn,880 in which the sodium hydroxide solution is replaced by pyridine, is an improvement on the Schotten-Baumann method ... 

The well-known Schotten-Baumann method of acylation569 is carried out in aqueous suspension, with an alkali hydroxide to bind the liberated acid. 

The various reactions that are involved in the Schotten-Baumann method of benzoylation are as given below ... 

This reaction was first reported by Schotten in 1884 and subsequently extended by Baumann in 1886. It is the acylation of alcohols and amines from acyl halide or anhydride in an aqueous alkaline solution (e.g., 1 M NaOH), and is generally known as the Schotten-Baumann reaction or Schotten-Baumann acylation. Occasionally, it is also referred to as the Schotten-Baumann method,or Schotten-Baumann esterification. Likewise, the formation of benzoyl ester under these conditions is called the Schotten-Baumann benzoylation." It is assumed that the reaction would perform well if carried out in a biphasic system of water and an immiscible organic solvent (e.g., CH2CI2), which has an important application in the acylation of amino acids.For example, p-nitrohippuric acid and dibenzoylornithine (ornithuric acid) all can be prepared under these conditions. 

A schematic of routes for the synthesis of amino acid surfactants is shown in Fig. la representative structures are illustrated in Fig. lb. The Schotten-Baumann method is a typical and useful way to synthesize A -acylamino acid. 

FIG. 3 Preparation of iV-acyglutamic acid by an improved Schotten-Baumann method, between the yield of iV-acyl-L-glutamic acid and solvent composition. (From Ref. 32.)... 

Schotten-Baumann method can generally be applied for the acylation of neutral amino acid to improve the reaction yield. 

A highly favorable reaction of two solutes (say at 0.1 m concentration) is usually much faster than a low-driving-force side reaction of one of the solutes with solvent water (55 m). The Schotten-Baumann method for making amides from acyl or sulfonyl halides in water is a well-known example. 

Obtained by partial esterification of 2,4-di-hydroxyphenyl 4-meth-oxybenzyl ketone with benzoyl chloride (Schotten-Baumann method) [5217]. 

The aminopyridines also undergo exocyclic acylation a, 220, 345, 359, 501-3, A second aroyl group can be introduced into 2-monoaroylaminopyridines, best by the Schotten-Baumann method, giving 2-diaroylaminopyri-dines ... 

The p-toluenesulphonate may alternatively be prepared by the Schotten-Baumann method (see below) substituting p-toluene-sulphonyl chloride for benzoyl chloride. 

Benzoate (especially for polyhydric phenols, but of general utility). The Schotten-Baumann method. 

In order to prepare benzoyl derivatives and substituted benzoyl derivatives on semimicro and micro scales, a cold suspension of an alkaline (5% NaOH) amine solution is shaken with a 2 — 3 fold excess of the chloride dissolved in a minimum amount of benzene. The derivative is isolated by evaporating the benzene. If this procedure is unsuccessful, the reaction is carried out by heating the components in pyridine. If the micropreparation is carried out by the Schotten-Baumann method, the reaction mixture should be neutralized after the reaction has stopped, in order to completely separate the benzoyl derivative of the type RCONHR. In view of the presence of a hydrogen atom on the nitrogen, the latter is partly soluble in the aqueous phase however, the pH of the solution should not drop below 8 (to prevent the precipitation of benzoic acid). 

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