Carboxylic acids and esters

In a carboxylic acid, the carbon atom of a carbonyl group on the first carbon is attached to a hydroxyl (—OH) group, which forms a carboxyl group. Some ways to represent the carboxyl group in propanoic acid follow. 

Write the lUPAC and common names for carboxylic acids and esters draw the condensed structural formulas when given their names. 

The lUPAC names of carboxylic acids replace the e in the corresponding alkane name with oic acid. If there are substituents, the carbon chain is numbered beginning with the carboxyl carbon. 

Methanoic acid 2-Methylpropanoic acid 3-Hydroxybutanoic acid 

As with the aldehydes, carboxylic acids with one to four carbon atoms have common names, which are derived from their natural sources. The common names use the prefixes of form, acet, propion, and butyr these common names are derived from Latin or Greek words (see Table 17.6). 

Carboxylic acids contain the —COOH functional group and are prepared by the oxidation of alcohols or aldehydes. These reactions occur quite easily, as evidenced by the souring of wine to form vinegar, which results from the oxidation of ethanol to acetic acid in the presence of oxygen from the air. 

All carboxylic acids are weak acids (see Section 9.2) and react with bases to form salts, for example. 

A number of carboxyhc acids are found in nature and have heen known for many years. As a result, some of the familiar carboxylic acids are almost always referred to by their common names (Table 14.6). 

Acetic acid, the acid found in about 5% concentration in vinegar, is produced in large quantities for use in making cellulose acetate, a polymer used in the manufacture of photographic film base, synthetic fibers, plastics, and other products (Section 14.5). 

Three other acids produced in large quantity have two carboxylic acid groups and are known as dicarboxylic acids. 

I AIM To learn the structures and names of the common carboxylic acids. 

Carboxylic acids are characterized by the presence of the carboxyl group, —COOH, which has the structure 

The general formula of a carboxylic acid is RCOOH, where R represents the hydrocarbon fragment. These molecules typically are weak acids in aqueous solution. That is, the dissociation (ionization) equilibrium 

Carboxylic adds can be produced by oxidizing primary alcohols with a strong oxidizing agent. For example, we can oxidize ethanol to acetic acid by using potassium permanganate. 

A carboxylic acid reacts with an alcohol to form an ester and a water molecule. For example, the reaction of acetic acid and ethanol produces the ester ethyl acetate and water. 

The preparation and reactivity of carboxylic acids and esters was outlined in CHEC-I, with particular emphasis on the ease and practical use of decarboxylation of acids (especially pyridazine- 

3-carboxylic acids), and the choice of esterification methods 84CHEC-I(3B)1 . The high acidity of the acids (e.g., pyridazine-4-carboxylic acid, pA 2.8) was also discussed. Some more illustrations of the chemistry of carboxylates are given here. 

Pyridazine-3,6-dicarboxylic acid undergoes facile decarboxylation in acid but esterification is successfully accomplished by adding thionyl chloride to alcoholic solutions of the diacid at — 30°C 

Ort/io-lithiated aniline derivatives can add to methyl 3-pyridazinecarboxylate to give ketones, though the yields are at best only moderate and reactions of the 4-analogue were still less successful 90JHC1645 . Similarly, addition of dilithiopyrazole to ethyl pyridazinecarboxylates gives 4-pyr-azolyl-3- and 4-pyridazinyl ketones (Equation (18)) tertiary alcohol formation is suppressed by inverse addition 91JHC1189 . 

Several Carboxylic Acids, Their Systematic Names, and Their Common Names Systematic Name Common Name 

Over nickel catalysts, aromatic carboxylic acids can be hydrogenated without difficulty as their sodium salts. Thus, e -179 and m-toluic acids,180 m-hydroxybenzoic acid,181 and tetrephthalic acid182 were hydrogenated to the corresponding saturated acids in high yields over Raney Ni at elevated temperatures and pressures. Examples are shown in eqs. 11.47 and 11.48. o-Toluic acid and terephthalic acid afforded the trans acids predominantly under these conditions. 

Aromatic esters are hydrogenated without solvent or in alcohol. Ethyl benzoate (eq. 11.49),11 ethyl phenyl acetate,183 methyl salicylate (eq. 11,50),86a and diethyl phthalate (eq. 11.51)183 were hydrogenated almost quantitatively to the corresponding cyclohexane derivatives over Ni-kieselguhr at 150-200°C. The hydrogenation of the ethyl 

The benzoic acid prepared by an air oxidation of toluene contains small amounts of various compounds that decrease the catalytic activity of platinum metal catalysts. The benzoic acid purified by sublimation is hydrogenated much more rapidly than an unpurified one. On a large scale, however, treatment of commercial benzoic acid with Pd-C at 100-200°C under high hydrogen pressure in a solvent for hydrogenation or, better, treatment with 0.2-10% (for benzoic acid) of concentrated sulfuric acid at 

Commercial terephthalic acid may be purified by methods similar to those used for the purification of benzoic acid185,186by treating the acid with Pd-C and hydrogen, for example, at 290°C and 8.9 MPa H2, in the presence of acid.194 

Hydrogenation of o-, m- and /j-hydroxybcnzoic acids over platinum catalysts is labile to hydrogenolysis to give cyclohexanecarboxylic acid.195 The proportion of hy-drogenolysis increases in the order ortho meta para, and it amounted to as much 

The condensed structural formula for carboxylic acids is RCOOH, and for esters it is RCOOR. The R groups in esters may be the same or different. 

Carboxylic acids and esters have the general formulas  

Common carboxylic acids and esters are shown here. 

A Acetic acid, a carboxylic add, is the active ingredient in vinegar. 

21 Identify the structural formulas of the functional groups that distinguish carboxylic acids and esters. 

22 Given the name (or structural diagram) of a carboxylic acid or ester, write the structural diagram (or name). 

23 Given the reactants (or products) of an esterification reaction, predict the 

Potassium permanganate, KMn04 is a strong oxidizing agent. 

Acetic acid is produced by the stepwise oxidation of ethanol, first to acetaldehyde and then to acetic acid  

While in CHEC(1984) 1984CHEC(2)1 there is an emphasis on decarboxylation reactions of pyridazinecarboxylic acids and the choice of esterification methods, in CHEC-II(1996) 1996CHEG-II(6)1 more examples of reactions with pyridazinecarboxylic esters appeared. More recently, the aminolysis of 1,2-diazinecarboxylic esters such as 

4- bis(methoxycarbonyl)pyridazino[4,5-, ]indole, l,4-bis(methoxycarbonyl)pyridazino[4,5-3]benzo[3]furan, 8-methyl- 

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Spanel P and Smith D 1998 SIFT studies of the reactions of FijO", NO and Ot with a series of volatile carboxylic acids and esters Int. J. Mass Spectrom. Ion Proc. 172 137-47... 

Reduces carbonyl, carboxylic acids and esters to alcohols... 

PREPARATION OF ALCOHOLS BY REDUCTION OF CARBOXYLIC ACIDS AND ESTERS... 

Longer bond in carboxylic acids and esters (HCOOH, 131.2) 135.8(5)... 

Pyrrole Carboxylic Acids and Esters. The acids are considerably less stable than benzoic acid and often decarboxylate readily on heating. However, electron-withdrawing substituents tend to stabilize them toward decarboxylation. The pyrrole esters are important synthetically because they stabilize the ring and may also act as protecting groups. Thus, the esters can be utilized synthetically and then hydrolyzed to the acid, which can be decarboxylated by heating. Often P-esters are hydrolyzed more easily than the a-esters. 

S. Patai, ed.. The Chemistry of Carboxylic Acids and Esters, John Wiley Sons, New York, 1969. 

Similarly, carboxylic acid and ester groups tend to direct chlorination to the / and v positions, because attack at the a position is electronically disfavored. The polar effect is attributed to the fact that the chlorine atom is an electrophilic species, and the relatively electron-poor carbon atom adjacent to an electron-withdrawing group is avoided. The effect of an electron-withdrawing substituent is to decrease the electron density at the potential radical site. Because the chlorine atom is highly reactive, the reaction would be expected to have a very early transition state, and this electrostatic effect predominates over the stabilizing substituent effect on the intermediate. The substituent effect dominates the kinetic selectivity of the reaction, and the relative stability of the radical intermediate has relatively little influence. 

Section 15.3 Alcohols can be prepared from carbonyl compounds by reduction of carboxylic acids and esters. See Table 15.3. 

Linearly annelated 3-phenyl-3//-5-ethyl-8-oxo-5,8-dihydrotriazolo[4,5-g]quin-oline-7-carboxylic acid and ester 173 were prepared starting from ethyl 7-chloro-6-... 

Carboxylic acids and esters of heterocyclic series including lactones 98JCS(P1)2451, 99JCS(P1)3537. 

Carboxylic acids and esters are reduced to give primary alcohols. 

The chemistry of carboxylic acids and esters The chemistry of the carbon-nitrogen double bond The chemistry of amides The chemistry of the cyano group The chemistry of the hydroxyl group (2 parts)... 

The Chemistry of Carboxylic Acids and Esters The Chemistry of the Carbon-Nitrogen Double Bond The Chemistry of the Cyano Group The Chemistry of Amides... 

Note that Lewis acidity decreases, whereas Brpnsted acidity increases, going down the table. There is no contradiction here when we remember that in the Lewis picture the actual acid in all Brpnsted acids is the same, namely, the proton. In comparing, say, HI and HF, we are not comparing different Lewis acids but only how easily F and 1 give up the proton. The effect discussed here is an example of a symmetry factor. For an extended discussion, see Eberson, L. in Patai The Chemistry of Carboxylic Acids and Esters, Wiley NY, 1969,... 

The reaction has been extended to ketones, carboxylic acids and esters (all of which couple a to the C=0 group), and amides (which couple a to the nitrogen) by running it in the presence of H2. ° Under these eonditions it is likely that the excited Hg abstracts H from H2, and that the remaining H- abstracts H from the substrate. 

For a review of the addition of thio acids, see Janssen, M.J. in Patai The Chemistry of Carboxylic Acids and Esters Wiley NY, 1969, p. 720. 

Pyrolysis of Carboxylic Acids and Esters of Carboxylic Acids... 

The choice of the alcohol permits manipulation of the structure of the polymer. Water and monohydric alcohols afford linear chains with carboxylic acid and ester end groups, respectively. Polyhydroxy initiators afford a route to ester end-blocked star and comb polymers (Fig. 4) (47). 

Figure 29 (a) Synthesis route of the molecule (b) (i) S8, NaOH, tetraethyleneglycol dimethyl ether, heat, (28%). (b) Adamantane upper rim derivative based on the thiacalix[4]arene platform. (c,d) The carboxylic acid and ester derivative of adamantane can also be used as substituents. Taken from Ref. [109] with permission. 

Nucleophilic substitutions of 0-activated 2-hydroxy carboxylic acids and esters, respectively, are well established, but little is known about the analogous reactions of activated cyanohydrins. Chiral 2-sulfonyloxynitriles, accessible from non-racemic cyanohydrins, have a relatively high configurational stability. They react with nucleophiles under very mild conditions under inversion of configuration (Scheme 8). ° ... 

Carbonyl compounds, such as aldehydes [103, 179], (thio)ketones [31, 94, 180-183], carboxylic acids, and esters [183, 184] with 1 are reduced to alcohols after hydrolysis [5], except in stericaUy hindered cases (see Section 8.5) [185, 186]. Under the same experimental conditions the regioselective reduction of the oxirane ring with 1 gives also the corresponding alcohol [183, 187]. 

In general, the methods for protection and deprotection of carboxylic acids and esters are not as convenient as for alcohols, aldehydes, and ketones. It is therefore common to carry potential carboxylic acids through synthetic schemes in the form of protected primary alcohols or aldehydes. The carboxylic acid can then be formed at a late stage in the synthesis by an appropriate oxidation. This strategy allows one to utilize the wider variety of alcohol and aldehyde protective groups indirectly for carboxylic acid protection. 

Carboxylic acids and esters can also be converted to amines with loss of the carbonyl group by reaction with hydrazoic acid, HN3, which is known as the Schmidt reaction,278 The mechanism is related to that of the Curtius reaction. An azido intermediate is generated by addition of hydrazoic acid to the carbonyl group. The migrating group retains its stereochemical configuration. 

Hydrogenolyses of carboxylic acids and esters to the corresponding aldehydes seems very attractive due to their simplicity. Copper chromites are the most widely used catalysts.15 Raney copper and zinc oxide-chromium oxide have also been used for this process.16-18 The hydrogenolysis of methyl benzoate to benzaldehyde was studied on various metal oxides at 300-350°C. ZnO, Zr02 and Ce02 presented high activities and selectivities (Scheme 4.8). 

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