Anhydrides acids

Anhydrides can be prepared by the reaction between a carboxyUc acid and an acid halide  

Notice that pyridine is used, once again, to remove the HCl that is formed as a by-product. We can avoid the need for pyridine by using a carboxylate ion (a deprotonated carboxylic acid) instead of a carboxylic acid  

Notice that the by-prodnct is NaCl, rather than HCl, so pyridine is no longer needed. 

Acid anhydrides are almost as reactive as acid hahdes. So, the reactions of acid anhydrides are very similar to the reactions of acid hahdes. Yon just have to train your eyes to see the leaving 

When a nucleophile attacks an acid anhydride, the carbonyl group can re-form to expel a leaving group that is resonance-stabilized  

Acid Anhydrides. - A polymer derived from 4-vinylpyridine has been found to be a very efficient catalyst for the formation of mixed anhydrides (91) from one equivalent each of a carboxylic acid and an 

A variety of substituted maleic anhydrides (93) are available from Michael additions of imidazo[1,2-a]pyridinium salts (92) to the 

Acid anhydrides have important commercial uses. One of the acid anhydrides of such importance is acetic anhydride. 

Acetic anhydride can be synthesized by reacting a compoimd called ketene with acetic acid. 

Cyclic anhydrides such as succinic anhydride, maleic anhydride, and glutaric anhydride can be prepared by heating the corresponding dicarboxylic acids. The reaction results in intramolecular dehydration and ring formation. Study the following example. 

Acid anhydrides are carboxylic acid derivatives formed by condensing two carboxylic acid molecules. 

Acid anhydrides are derived from acids by removing water from two carboxyl groups and connecting the fragments. 

The most important commercial aliphatic anhydride is acetic anhydride (R=CH3). About 1 million tons are manufactured annually, mainly to react with alcohols to form acetates. The two most common uses are in making cellulose acetate (rayon) and aspirin (acetylsalicylic acid). 

The name of an anhydride is obtained by naming the acid from which it is derived and replacing the word acid with anhydride. 

PROBLEM 10.26 Write the structural formula for a. butanoic anhydride b. benzoic anhydride 

Acid anhydrides of general formula RCO-O-COR react with water, yielding the corresponding acid. While this reaction is rapid with acetic anhydride, it becomes very slow as the molecular mass of the anhydride increases. These are intermediates for organic synthesis. As an example, acetic anhydride is used for the fabrication of cellulose acetates. 

At room temperature, the dissolution rate is 0.05 mm per year. At 50 °C, the decrease in thickness of aluminium is 0.50 mm per year, and 1.25 mm per year at the boiling point of pure anhydride (136 °C). 

Mixtures of acetic acid and acetic anhydride at any ratio have only a very slight action on aluminium. At ambient temperature, the decrease in thickness is less than 0.05 mm per year[13].Attheboilingpointof mixtures containing more than 10 wt% of acetic acid, the attack of aluminium becomes significant. 

Acetic anhydride will be neither altered nor discoloured in contact with aluminium. Exchangers and reaction vessels in aluminium are commonly used in production units for this product. It is stored and transported in aluminium drums and tanks. 

2 Reactions of Acid Anhydrides 3.18.2.1 Hydroylsis (Acid Formation) 

4 Friedel-Crafts Acylation (Ketone Formation) (RC0)20 + ArH RCOAr + RCOOH 

Loss of water from two molecules of a carboxylic acid results in an acid anhydride. Anhydride means without water. An anhydride is a carboxylic acid derivative, because the OH of a carboxylic acid has been replaced by a carboxylate ion. 

If the two carboxylic acid molecules forming the acid anhydride are the same, then the anhydride is a symmetrical anhydride. If they are different, then it is a mixed anhydride. Symmetrical anhydrides are named by replacing acid in the acid name with anhydride. Mixed anhydrides are named by stating the names of both acids in alphabetical order, followed by anhydride.  

CH3 O ri3 ethanoic anhydride acetic anhydride a symmetrical anhydride 

The leaving group of an anhydride is a carboxylate ion (its conjugate acid has a p a of 5), which means that an anhydride is less reactive than an acyl chloride but more reactive than an ester or a carboxylic acid. 

Therefore, an acid anhydride reacts with an alcohol to form an ester and a carboxylic acid, with water to form two equivalents of a carboxyhc acid, and with an amine to form an amide and a carboxylate ion. In each case, the incoming nucleophile—after it loses a proton—is a stronger base than the departing carboxylate ion. (Recall that a carboxylic acid derivative can be converted to one that is less reactive but not to one that is more reactive.) 

Note that the diorganocopper reaction occurs only with acid chlorides. Carboxylic acids, esters, acid anhydrides, and amides do not react with Uthlirm diorganocopper reagents. 

How could you prepare the following ketones by reaction of an acid chloride with a lithium diorganocopper reagent  

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Both symmetrical and unsymmetrical acid anhydrides can be prepared in this way. 

Only a limited amount of work has been published concerning the reactions of phosgene with carboxylic acid anhydrides, despite the fact that the product acid chlorides, formed as illustrated in Equation (10.23), are generated without concomitant formation of co-product hydrogen chloride, as in the case for the corresponding reaction of the carboxylic acids. 

Reaction (10.23) (R = Me, Bu, MejCHCH, or Ph) may be catalysed by 7V,A/-dialkyl-carboxamides, such as dmf, at between 40 and 150 C [388]. Using iron(III) catalysts, such as iron(IIl) chloride, in a sealed tube, the intramolecular anhydrides were efficiently converted into their acid chlorides [278a]  

Both anhydride and acid functions were converted into -C(0)Ci groups when phosgene was passed into a solution of (10.27 R = COOH) in benzene containing dmf at 65 C [1415,2084]. 

Another interesting example of catalysis by dmf involves the reaction of phosgene with isatoic anhydride [2087c]  

2-lsocyanatobenzoic acid is the most likely intermediate of this reaction [2087c]. 

The binary oxygen compounds of the non-metallic elements tend to produce acidic solutions when they are added to water. Compounds such as SO3, CO2, and P4O6 are sometimes referred to as the acid anhydrides ( acids without water ). 

In some cases, the reaction involves more than simply incorporating the elements of water. Thus nitrogen dioxide, used in the commercial preparation of nitric acid, is not an anhydride in the strict sense  

Symmetrical (but not unsymmetrical) anhydrides are useful acylating reagents as milder alternatives to acyl halides. The most convenient procedure for their preparation involves the interaction in benzene solution of the acyl halide with the corresponding carboxylic acid in the presence of pyridine, which removes the hydrogen chloride liberated as the insoluble pyridinium chloride. 

Without pyridine, anhydride formation would be incomplete, as a result of an equilibrium reaction of the anhydride with hydrogen chloride which regenerates the acyl chloride and the carboxylic acid. 

Mixed anhydrides (i.e. R COOCOR2) can also be readily prepared by this general route by choosing appropriate reactants. 

The reaction of keten with a carboxylic acid gives a mixed anhydride as the first formed product. 

Slow distillation at atmospheric pressure of the mixed anhydride with a second molar proportion of the carboxylic acid yields the symmetrical anhydride and acetic acid. 

When succinic anhydride was hydrogenated over palladium catalysts, y-butyrolactone was produced in high yield in ethyl acetate at 30-95°C and 7.3-10.8 MPa H2 (eq. 10.34).61 

McAlees et al. studied the hydrogenation of various phthalic anhydrides over 10% Pd-C in ethyl acetate.62 Hydrogenation of phthalic anhydride gave o-toluic acid in high yield. Either 3- or 4-substituted phthalic anhydrides may give phthalides and/or 2-(hydroxymethyl)benzoic acids in addition to o-toluic acids. In the case of 4-methoxyphthalic anhydride, the product mixture contained 35% of 2-(hydroxymethyl)- 

Maleic anhydride can be hydrogenated to the industrially important compounds y-butyrolactone and tetrahydrofuran. Hydrogenolytic cleavage of the C-0 bond on Cu-based multicomponent catalysts is much easier in y-butyrolactone than in tetrahydrofuran [28]. 

Aromatic amines usually require an elevated temperature cure. Epoxies cured with aromatic amines usually have a longer working life than epoxies cured with aliphatic amines. These curing agents are relatively difficult to use because they are solids and must be melted into the epoxy. However, the allowable operating temperature for epoxies cured with aromatic amines are higher than those epoxies cured with aliphatic amines. 

These are widely used because the curing of the epoxies takes place at room temperature. High exothermic temperatures develop during the curing reaction that limit the mass of material that can be cured. The electrical and physical properties of these aliphatic-cured resins had the greatest tendency toward degradation of electrical and physical properties at elevated temperatures. Typical aliphatic amines used include diethylene triamine (DETA) and triethylene tetramine (TETA). 

Catalytic curing agents require a temperature of 200°F (93°C) or higher to react. These epoxy formulations exhibit a longer working life than the aliphatic amine cured epoxies. The exothermic reaction may be critically affected by the mass of the resin mixture. Typical materials used include piperidine, boron trifluoride ethylamine complex, and benzyl dimethyl-amine (BDMA). 

These curing agents are becoming more widely used because they are easy to work with, have minimmn toxicity problems compared with amines, and offer optimum high-temperature properties to the cured resin. Typical acid 

The epoxy resin family exhibits good resistance to alkalies, non-oxidizing acids, and many solvents. Typically, epoxies are compatible with the following materials at 200°F (93 C) imless otherwise noted  

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Phosphorus(V) oxide will remove water from acids to give the acid anhydride. For example, if nitric acid is distilled with it. dinitrogen pentoxide is formed ... 

If chlorine water is boiled the chloricfl) acid decomposes as above, but a little may break down into steam and the acid anhydride, dichlorine monoxide ... 

Required Acetic acid/anhydride mixture, 20 ml. aniline, 10 ml. 

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... 

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. 

B) ACID ANHYDRIDES. Acetic anhydride, succinic anhydride phthalic anhydride (and substituted derivatives). 

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

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. 

Acid anhydrides Carbohydrates Quinones Hydrocarbons Ethers... 

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. 

ACID ANHYDRIDES OF ALIPHATIC CARBOXYLIC ACIDS Acid anhydrides of monobasic aliphatic acids may be prepared —... 

The physical properties of a number of acid anhydrides (aliphatic) are given in Table 111,94. 

Perkin reaction. The condensation of an aromatic aldehyde with an acid anhydride in the presence of the sodium or potassium salt of the acid... 

By the Friedel and Crafts reaction. The condensation of an acid chloride or an acid anhydride with an aromatic hydrocarbon in the presence of anhydrous aluminium chloride generally gives a good yield of the aromatic ketone ... 

The use of aliphatic acid anhydrides in place of acid chlorides offers many advantages these include ... 

With acid anhydrides, an acyl chloride is probably formed first ... 

AROMATIC ACID ANHYDRIDES The anhydrides of aromatic acids are prepared —... 

In a modification the acid chloride is treated with excess of dry pyridine whereby the addition complex ArCOCl. CgHjN is formed decomposition of the latter with water aflFords the acid anhydride ... 

The physical properties of a few tjrpical acid chlorides of aromatic acids are collected in Table IV, 18 7). Some acid anhydrides are also included in this Table (compare Section 111,94). 

A ketone having an a-hydrogen atom may be acylated with an eater or an acid anhydride to form a p diketone ... 

The acylation of ketones with acid anhydrides may be effected by means of the acid reagent boron trifluoride, for example ... 

A mixture of an acid anhydride and a ketone is saturated with boron trifluoride this is followed by treatment with aqueous sodium acetate. The quantity of boron trifluoride absorbed usually amounts to 100 mol per cent, (based on total mola of ketone and anhydride). Catalytic amounts of the reagent do not give satisfactory results. This is in line with the observation that the p diketone is produced in the reaction mixture as the boron difluoride complex, some of which have been isolated. A reasonable mechanism of the reaction postulates the conversion of the anhydride into a carbonium ion, such as (I) the ketone into an enol type of complex, such as (II) followed by condensation of (I) and (II) to yield the boron difluoride complex of the p diketone (III) ... 

Acid Chlorides and Acid Anhydrides of Aromatic Adda, Table IV, 187. Aliphatic Esters, Table III, 106. 

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