Thionyl chloride with carboxylates

The reaction of thionyl chloride with carboxylic acids yields either acid chlorides or, in some cases, anhydrides depending on the stoichiometry... 

Thionyl chloride (39) in the presence of a few drops of DMF (catalyst) is a valuable reagent for the conversion of sulfonic acids (31) into the sulfonyl chlorides (32) (Scheme 32). This resembles the well-known reaction of thionyl chloride with carboxylic acids for the preparation of acyl chlorides, and has the advantage that both the by-products are gaseous. 

Eormulate a suitable mechanism to account for the reaction of thionyl chloride with carboxylic acids to yield the corresponding chlorosulfite (see the reaction diagrammed in the discussion section). Hint The first step is the nucleophilic attack of the oxygen of the —OH group of the acid on the sulfur atom of the S=0 group of the thionyl chloride. 

Thiiranes (episulfides) have been suggested as intermediates in the reaction of thionyl chloride with various substrates including ketones and carboxylic acids.54 However, apart from one claim, later corrected, no such compounds have been isolated.55,56... 

The addition of hydrogen bromide and sulfur dioxide to phenylpropiolic acid (210) in diethyl ether at -50 °C is reported to give 3-bromobenzo[6]thiophene-2-carboxylic acid (211) (75ZOR1776). If hydrogen bromide and sulfur dioxide can react under these conditions to give thionyl bromide, the reaction is similar to the reaction of thionyl chloride with unsaturated acids, reported in the previous section. 

Carboxylic acids react with phosphorus trichloride, phosphorus pentachloride, or thionyl chloride with replacement of OH by Cl to form acyl chlorides, RCOC1 ... 

For acylation in pyridine by Einhorn s method it is not always necessary to start with preformed acyl chloride. Its preparation and reaction can be effected in one operation by dissolving the amine and carboxylic acid together in pyridine, adding the calculated amount of thionyl chloride with cooling, and after some time pouring the mixture into water the amide is precipitated and is washed successively with dilute acid, dilute alkali hydroxide, and water. 

Suppose you are trying to synthesize the dipeptide Val-Ser. Compare the product that would be obtained if the carboxyl group of N-protected valine were activated with thionyl chloride with the product that would be obtained if the carboxyl group were activated with DCC. 

A NEW REACTION OF THIONYL CHLORIDE WITH A CARBOXYLIC ACID IN THE PRESENCE OF A TERTIARY AMINE. AN X-RAY CRYSTALLOGRAPHIC PROOF OF STRUCTURE OF ALPHA-CHLORO-ALPHA-CHL0R0SULFENYL4-NITR0-2,... 

The mechanism for the reaction of thionyl chloride with a carboxylic acid to form an acid chloride is similar to that presented in Section 10.5C for the conversion of an alcohol to a chloroalkane and involves initial chlorosulfite formation, followed by nucleophilic attack of chloride ion on the carbonyl carbon to give a tetrahedral carbonyl addition intermediate, which decomposes to give the acid chloride, SO2, and chloride ion. 

Ethyl cyctopropane-carboxylate. Use 22 g. of cyciopropane-carb-oxyhc acid (Section V,33) and 40 g. (24-5 ml.) of redistiUed thionyl chloride to prepare the acid chloride, b.p. 118-119° (22 g.). Treat the latter with 10-1 g. of absolute ethyl alcohol. The yield of ethyl cyclo-propane-carboxylate, b.p. 132-133°, is 13 g. 

Acyl chlorides are readily available They are prepared from carboxylic acids by reaction with thionyl chloride... 

Thionyl chloride reacts with carboxylic acids to yield acyl chlorides... 

Orotic acid undergoes 5-nitration, 5-bromination in hydrobromic acid with peroxide, 5,5-dibromination following decarboxylation in bromine water, esterification, methylation (rather complicated), conversion into its acid chloride (containing some anhydride) by treatment with thionyl chloride, and conversion into 2,6-dichloropyrimidine-4-carboxylic acid by phosphoryl chloride (62HC(16)422). 

Properly substituted isoxazolecarboxylic acids can be converted into esters, acid halides, amides and hydrazides, and reduced by lithium aluminum hydride to alcohols. For example, 3-methoxyisoxazole-5-carboxylic acid (212) reacted with thionyl chloride in DMF to give the acid chloride (213) (74ACS(B)636). Ethyl 3-ethyl-5-methylisoxazole-4-carboxylate (214) was reduced with LAH to give 3-ethyl-4-hydroxymethyl-5-methylisoxazole (215) (7308(53)70). 

In a first step, the carboxylic acid 1 is converted into the corresponding acyl chloride 2 by treatment with thionyl chloride or phosphorous trichloride. The acyl chloride is then treated with diazomethane to give the diazo ketone 3, which is stabilized by resonance, and hydrogen chloride ... 

The 3-o-ch orophenvl-5-methvlisoxa2ole4-carboxylic acid, from which the acid chloride was prepared, was obtained by hydrolysis of the ester product of the reaction between o-chloro-benzohydroxamic chlorideand ethyl acetoacetate in methanolic sodium methoxide. Reaction with thionyl chloride gave the starting material. 

To a suspension of 12.0 grams of 3-methylflavone-8-carboxylic acid in 200 ml of anhydrous benzene Is added 10.0 grams of thionyl chloride. The mixture is refluxed for 2 hours during which the suspended solid goes into solution. The solvent is completely removed by distillation, the residue extracted with benzene and the extract evaporated to dryness. The product, 3-methylflavone-8-carboxylic acid chloride, is recrystallized from ligroin to give crystals melting at 155° to 156°C. 

Methyl pyrazine-2-carboxylic acid is refluxed with thionyl chloride in anhydrous benzene for approximately 12 hours. Benzene and thionyl chloride excess is removed by distillation. Then some anhydrous dioxane is added and this acid chloride solution is allowed to drop into p-(/3-aminoethyl)-benzenesulfonamide suspension in dioxane and anhydrous pyridine. The resulting mixture is then refluxed for 3 hours. Dioxane is removed by distillation and then the residue is washed with water and acetic acid. The raw acylated sulfonamide is then filtered and crystallized from 95% ethanol, thus obtaining a product of MP 200 to 203 C. 

Acid chlorides are prepared from carboxylic acids by reaction with thionyl chloride (SOCl2), as we saw in the previous section. Similar reaction of a carboxylic acid with phosphorus tribromide (PB ) yields the acid bromide. 

Benzothiepins synthesized by a double Knoevenagel condensation (see Section 2.1.1.2.) contain free carboxylic acid groups if the reaction product is isolated under acidic conditions. Rcesterification can be performed by two methods via formation of the acid chloride and subsequent alcoholysis, or by reaction with diazomethane, e.g. the conversion of 3-benzo-thiepin-2,4-diearboxylic acid (5, R = C02H) with thionyl chloride and methanol gives the dimethyl ester 5 (R = C02Me) in 47% yield, while the diazomethane pathway provides 60% of the dimethyl ester.65 Use of excess diazomethane leads to cycloadducts (see Section 2.2.4.). 

Treatment of phthalocyaninesulfonic or -carboxylic acids with chlorinating agents such as phosphorus pentachloride or thionyl chloride leads to the corresponding acid chlorides, e.g. 7. 

Aziridine-2-carboxylates 12 (Scheme 3.4) have also been prepared from 3-hy-droxy-a-amino esters 9 by treatment with sulfuryl chloride in place of tosyl or mesyl chloride. Treatment of 9 with thionyl chloride in the presence of triethylamine, followed by oxidation of 10 with sodium periodate and a catalytic amount of... 

Thionyl chloride is another activating agent employed for reactions between aromatic carboxylic acids and phenols in pyridine solution. The mechanism suggested does not involve the formation of an acid chloride but assumes the existence of an intermediary mixed sulfinic anhydride which undergoes reaction with phenolic endgroups (Scheme 2.32).311... 

Many procedures for the formation of carboxylic acid amides are known in the literature. The most widely practiced method employs carboxylic acid chlorides as the electrophiles which react with the amine in the presence of an acid scavenger. Despite its wide scope, this protocol suffers from several drawbacks. Most notable are the limited stability of many acid chlorides and the need for hazardous reagents for their preparation (thionyl chloride, oxalyl chloride, phosgene etc.) which release corrosive and volatile by-products. Moreover, almost any other functional group in either reaction partner needs to be protected to ensure chemoselective amide formation.2 The procedure outlined above presents a convenient and catalytic alternative to this standard protocol. 

In analogy to the well-known condensation products of fatty acids with protein hydrolysates, a patent has also been initiated for the condensation products of ether carboxylic acids and protein hydrolysates [43]. They are made by converting the ether carboxylic acids with thionyl chloride (SOCl2) to the corresponding acid chlorides followed by the condensation with a protein hydrolysate. 

The traditional method for transforming carboxylic acids into reactive acylating agents capable of converting alcohols to esters or amines to amides is by formation of the acyl chloride. Molecules devoid of acid-sensitive functional groups can be converted to acyl chlorides with thionyl chloride or phosphorus pentachloride. When milder conditions are necessary, the reaction of the acid or its sodium salt with oxalyl chloride provides the acyl chloride. When a salt is used, the reaction solution remains essentially neutral. 

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