Chlorides acids

Acid chlorides show a very strong band for the C=0 group that appears in the range of 1810-1775 cm for aliphatic acid chlorides. Acid chloride and anhydrides are the most common functional groups that have a C=0 appearing at such a high frequency. Conjugation lowers the frequency. 

C=0 Stretch occurs in the range 1810-1775 cm in unconjugated chlorides. Conjugation lowers the frequency to 1780-1760 cm .  

FIGURE 2.56 The infrared spectrum of benzoyl chloride (neat liquid, KBr plates). 

In some aromatic acid chlorides one may observe another rather strong band, often on the lower-frequency side of the C=0 band, which makes the C=0 appear as a doublet. This band, which appears in the spectrum of benzoyl chloride (Fig. 2.56) at about 1730 cm is probably a Fermi resonance band originating from an interaction of the C=0 vibration, with an overtone of a strong band for 1-C stretch often appearing in the range from 900 to 800 cm . When a fundamental vibration couples with an overtone or combination band, the coupled vibration is called Fermi resonance. The Fermi resonance band may also appear on the higher-frequency side of the C=0 in many aromatic acid chlorides. This type of interaction can lead to splitting in other carbonyl compounds, as weU. 

C—Cl Stretching Vibrations. These bands, which appear in the range from 730 to 550 cm are best observed if KBr plates or cells are used. One strong C—Cl band appears in the spectrum of acetyl chloride. In most other acid chlorides, one may observe as many as four bands, due to the many conformations that are possible. 

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Amide Ester Acid anhydride Acid chloride 

An acid chloride can be prepared by using thionyl chloride and the corresponding carboxylic acid. 

111 this approach, formation of an acid chloride is required to activate the carbonyl group and make it more electrophilic. This activation is required in most transformations of carboxylic acids because carboxylic acids themselves are not sufficiently electrophilic to react with most nucleophiles. Furthermore, since many nucleophiles are also basic, they can react with carboxylic acids to give the car-boxylate ion, which is an even poorer electrophile than the carboxylic acid itself. 

Amides are also available from nitriles, which have the same oxidation level. Direct acid or base hydrolysis of a nitrile usually requires fairly severe conditions and often does not stop at the amide stage but goes on the carboxylic acid. Treatment of nitriles with a solution of HC1 in ethanol furnishes an imidate ester which is hydrolyzed in aqueous acid to the amide. Because a nitrile is the starting material, only primary amides can be produced by this process. 

Traditional textbook preparations of acid chlorides from carboxylic acids include 

The traditional methods utilize sulfur or phosphorous halides to convert the acid to die acid chloride. Of these methods, thionyl chloride [often with a catalytic amount of dimethyl formamide (DMF)] is the most useful since the by-products of die reaction are gases (SO2, HC1) which can be easily purged from the reaction mixture with a stream of nitrogen. The acid chloride product can then be purified on a small scale by bulb-to-bulb distillation or crystallization. Because an excess of thionyl chloride is usually used, there must be a purification step to remove the excess reagent. 

Another superior reagent for the preparation of acid chlorides is oxallyl chloride in methylene chloride. Addition of a carboxylic acid leads to the smooth evolution of gas (CO2, CO, HC1) which can be used as a crude monitor of the reaction progress. The acid chloride is very easily purified since oxallyl chloride boils at 62°C and is easily evaporated from the product. In many instances, the crude product is sufficiently pure to be used directly. 

The reduction of acid chlorides is particularly easy however, by carefully adjusting the reaction conditions, the reduction process can be controlled. Starting from acid chlorides, aldehydes can be obtained by four different methods [C5, M3]  

The selective reduction of acid chlorides in the presence of esters by 9-BBN in cold THF is possible because esters are reduced only under reflux in this solvent [PSl], Reduction by Zn(BH4)2 TMEDA in Et20 leaves Cl, NO2, ester groups, and conjugated double bonds unchanged [KU3]. 

Although this is an interesting concept and may find specific applications, the overall process does not yet offer a great advantage from an environmental standpoint, as the production of acyl chlorides is particularly waste-intensive. 

5 Ketone Formation by Reaction with Organocadinm Componnds 

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Sulphur oxide dichloride is used as a chlorinating agent in organic chemistry, for example in the preparation of acid chlorides ... 

Esters can also be prepared by the action of alcohols on acid chlorides and anhydrides. 

It should be emphasised that whereas the interaction of a sodium salt and an acid chloride is a convenient general laboratory method for preparing all classes of anhydrides, acetic anhydride is prepared on a large scale by other and cheaper methods. Industrial processes are based on reactions indicated by the equations ... 

Method (1) is most frequently used for aliphatic acid amides, while Methods (2a), (2b) and (zc) are used most frequently for aromatic acid amides. Of the last three methods, the Acid Chloride Method (zb) is the most rapid and certain. The Ester Method (za) is practicable only when the amide is insoluble in water, and even then is often very slow unless the ester itself is appreciabb soluble in the aqueous ammonia solution. 

It will also reduce acid chlorides, acid anhydrides and aldehydes to primary alcohols, ketones to secondary alcohols, and amides to the corresponding amines R-CONHi -> R CHiNH. Nitro-hydrocarbons if aromatic are... 

One of the general methods for the preparation of acid chlorides is the action of phosphorus pentachloride on the corresponding carboxylic acid ... 

One disadvantage of this method is that it is sometimes difficult to separate the acid chloride sharply from the phosphorus oxychloride by fractional dis tillation, and unless the boiling oints of these two substances are fairly wide apart, traces of the oxychloride will occasionally pass over in the vapour of the acid chloride. If, however, thionyl chloride is used instead of phosphorus... 

The Schotten-Baumann reaction may also be carried out, using, for example, benzene sulphonyl chloride, CeH,SO,Cl (. e., the acid chloride of benzene sulphonic acid, C H5SOjOH) in place of benzoyl chloride, and similar deri a-tives are obtained. Thus when phenol is dissolved in an excess of 10% sodium hydroxide solution, and then shaken with a small excess of benzene sulphonyl... 

Esters (a) and acid chlorides (6) readily react with Grignard reagents to give ketones, which immediately react with a second equivalent of the reagent as in (5) to give tertiary alcohols as before. 

The preparation of acetophenone (p. 255) is a modification of this method, the alkyl halide being replaced by an acid chloride, with the consequent formation of a ketone. 

Hydroxamic acid formation resembles amide formation (pp. 117-119) and therefore certain other classes of substances will respond to the test, e.g., acid chlorides and acid anhydrides, but these substances are readily distinguished by other reactions. 

A similar coloration is given by acid chlorides, acid anhydrides. ind many amides, but these classes of substances are readily detected by other means and cannot be confused with esters. 

A) ACID CHLORIDES. Acetyl chloride benzoyl chloride (and substituted benzoyl chlorides). 

The chemical reactions of the acid chlorides and anhydrides are so closely parallel that they are considered together. 

Acid chlorides (but not acid anhydrides) precipitate silver chloride on treatment with aqueous AgNOg acidified with HNO3-... 

Acid chlorides, and some anhydrides, condense with aniline to give anilides. 

Acid chlorides and anhydrides give hydroxamic acids with... 

Action of silver nitrate. Acidify 2 ml. of aqueous AgNOj solution with dil. HNO3 and add the acid chloride drop by drop with shaking. Acetyl chloride and benzoyl chloride give a precipitate of AgCl. Filter, wash with water, and then with methylated spirit to remove any benzoic acid the AgCl remains. 

The choice of type of derivative should be based on whether the chloride or anhydride is aliphatic or aromatic, because this factoi largely determines the reactivity. Aliphatic acid chlorides are best converted into their anilides, as in 4 above aromatic acid chloride may be similarly converted into their anilides, or they may be converted into their amides by shaking with an excess of ammonia (p, 120). (M.ps., pp. 544-545.) Aliphatic acid anhydrides should be converted into their crystalline anilides, but aromatic acid anhydrides arc best hydrolysed to the acid, which can then be converted into one of the standard derivatives (p. 349). 

Almost insoluble in cold water. Higher alcohols (including benzyl alcohol), higher phenols (e.g., naphthols), metaformaldehyde, paraldehyde, aromatic aldehydes, higher ketones (including acetophenone), aromatic acids, most esters, ethers, oxamide and domatic amides, sulphonamides, aromatic imides, aromatic nitriles, aromatic acid anhydrides, aromatic acid chlorides, sulphonyl chlorides, starch, aromatic amines, anilides, tyrosine, cystine, nitrocompounds, uric acid, halogeno-hydrocarbons, hydrocarbons. 

Reacts slowly on heating without evolution of gas. Esters some acid chlorides and anhydrides benzaldehyde (undergoes Cannizzaro s reaction, p. 342). 

L. Treat with hydroxylamine and ferric chloride (pp. 334, 353). Violet or red colorations given particularly by esters. Deep colorations also given by acid chlorides, acid anhydrides and by some acid amides (usually aliphatic) and by a few of the simpler anilides. 

Corrosive liquids and solids (acids, acid chlorides, etc.) are easily manipulated, and no impurities are introduced into the product from the apparatus. 

The acid chloride is available commercially, but it is more economical to prepare it from the acid as and when required. Furthermore, 3 5-dini-trobenzoyl chloride tends to undergo hydrolysis if kept for long periods, particularly if the stock bottle is frequently opened. The substance may, however, be stored under light petroleum. 

Amides, anilides and p toluidides. The dry acid is first converted by excess of thionyl chloride into the acid chloride ... 

The by-products are both gaseous and the excess of thiouyl chloride (b.p. 78°) may be readily removed by distillation. Interaction of the acid chloride with ammonia solution, aniline or p-toluidiiie yields the amide, anilide or p-toluidide respectively ... 

Stopper the side arm of a 25 or 50 ml. distilling flask and fit a vertical water condenser into the neck. Place 0-5-1 -0 g. of the dry acid (finely powdered if it is a solid) into the flask, add 2-5-5 0 ml. of redistilled thionyl chloride and reflux gently for 30 minutes it is advisable to place a plug of cotton wool in the top of the condenser to exclude moisture. Rearrange the condenser and distil off the excess of thionyl chloride t (b.p. 78°). The residue in the flask consists of the acid chloride and can be converted into any of the derivatives given below. 

Amides. TVeat the acid chloride cautiously with about 20 parts of concentrated ammonia solution (sp. gr. 0 - 88) and warm for a few moments. If no solid separates on cooling, evaporate to dryness on a water bath. Recrystallise the crude amide from water or dilute alcohol. 

Alternatively, dissolve or suspend the acid chloride in 5-10 ml. of dry ether or dry benzene, and pass in dry ammonia gas. If no solid separates, evaporate the solvent. Recrystallise the amide from water or dilute alcohol. 

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