Naming Carboxylic Acids and Nitriles

Simple carboxylic acids derived from open-chain alkanes are systematically named by replacing the terminal -e of the corresponding alkane name with -ok acid. The —CO9H carbon atom is numbered Cl. 

Propanoic acid 4-M thylpentanoic acid 3-EthyI-6-methyloctanedioic acid 

Compounds containing the —C=N functional group are calleo nitriles and undergo some chemistry similar to that of carboxylic acids. Simple open-chain nitriles are named by adding -nitrile as a suffix to the alkane name, with the nitrile carbon numbered Cl, 

Nitriles can also be named as derivatives of carboxylic acids by replacing the -ic acid or -ok acid ending with -onitrile, or by replacing the -caiboxylic acid ending with -carbonitrile. The nitrile carbon atom is attached to Cl but is not itself numbered. 

Problem 20.1. Give lUPAC names for the following compounds  

Approximately 5 million metric tons of acetic acid is produced worldwide each year for a variety of purposes, including preparation of the vinyl acetate polymer used in paints and adhesives. About 20% of the acetic acid synthesized industrially is obtained by oxidation of acetaldehyde. Much of the remaining 80% is prepared by the rhodium-catalyzed reaction of methanol with carbon monoxide. 

Why This Chapter Carboxylic acids are present in many industrial processes and most biological pathways and are the starting materials from which other acyl derivatives are made. Thus, an understanding of their properties and reactions is fundamental to understanding organic chemistry. We ll look both at acids and at their close relatives, nitriles (RC = N), in this chapter and at carboxylic acid derivatives in the next chapter. 

Because many carboxylic acids were among the first organic compounds to be isolated and purified, a large number of common names exist (Table 20.1). Biological chemists, in particular, make frequent use of these names, so you may find yourself referring back to this list on occasion. We ll use systematic names in this book, with a few exceptions such as formic (methanoic) acid and 

Also listed in Table 20.1 are the names of acyl groups (r—C—) derived from the parent acids. Except for the eight entries at the top of Table 20.1, whose names have a -yl ending, all other acyl groups are named using an -oyl ending. 

Thomson -iCvV Click Organic Interactive to use a web-based palette to draw structures of carboxylic acids based on their lUPAC names. 

Propanoic acid 4-iVlethylpentanoic acid 3-Ethyl-6-methyloctanedioic acid 

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A common system of naming nitriles takes the name of the corresponding carboxylic acid and changes the suffix -oic to -onitrile ... 

A molecule bearing the COOH (carboxyl) unit (see Chapter 16, Section 16.4) is a carboxylic acid, and the name of 27 must reflect this fact. Compormd 27 is benzoic acid, the parent structure for this class. The usual acid derivatives, such as esters (benzoates), acid chlorides (benzoyl chlorides), and amides (ben-zamides), are all known, prepared by methods discussed in Chapter 20. There are also nitrile derivatives, and 28 is named benzonitrile. 

The functional group of a nitrile is a cyano (C=N) group bonded to a carbon atom. lUPAC names follow the pattern alkanenitrile (e.g., ethanenitrile). Common names are derived by dropping the suffix -ic or -oic acid from the name of the parent carboxylic acid and adding the suffix -onitrile. 

Whereas for most compound classes the exemplifications in Table 8 are directly applicable without any difficulty, the two alternative naming methods for aliphatic carboxylic acids and their derivatives as well as for nitriles and aldehydes require more detailed illustration. 

Salts and esters of carboxylic acids and related compounds are named by placing the name of the metal or the esterifying group in front of the name of the acid anion, separated by a space. Joint occurrence of both functions is indicated accordingly. Acid salts and esters are named analogously. Complex cases can also be named more descriptively ... salt or. .. ester of. .. acid. (Similar provisions are valid for other acid derivatives such as amides and nitriles.)... 

Nitriles are classified as carboxylic acid derivafives because fhey are convened fo car boxylic acids on hydrolysis The condifions required are similar fo fhose for fhe hydrol ysis of amides namely healing m aqueous acid or base for several hours Like fhe hydrolysis of amides nilrile hydrolysis is irreversible m fhe presence of acids or bases Acid hydrolysis yields ammonium ion and a carboxylic acid... 

Nitriles are classified as carboxylic acid derivatives because they are converted to carboxylic acids on hydrolysis. The conditions required are similar- to those for the hydrolysis of amides, namely, heating in aqueous acid or base for several hours. Like the hydrolysis of amides, nitrile hydrolysis is ineversible in the presence of acids or bases. Acid hydrolysis yields fflnmonium ion and a carboxylic acid. 

Solvents can be classified into three categories according to their polarity namely, polar protic, dipolar aprotic and non-polar. Most of the common solvents fall under one of following chemical classes Aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, phenols, ethers, aldehydes, ketones, carboxylic acids, esters, halogen-substituted hydrocarbons, amines, nitriles, nitro-derivatives, amides and sulfur-containing solvents (Marcus, 1998). In certain cases a mixture of two or more solvents would perform better than a single solvent. 

The suffixes -oic acid, -al, -amide and -nitrile are used to name acyclic compounds having one or two characteristic groups. Locants are not necessary, as these groups must be at the end of a chain. The suffixes -carboxylic acid, -carbaldehyde, -carboxamide and -carbonitrile are used when more than two groups are attached to chains or one or more groups are attached to cycles. 

Retained names of carboxylic acids may also be modified to name amides, nitriles and aldehydes, by changing the -ic acid ending to -amide, -onitrile or -aldehyde. Names such as formaldehyde, acetonitrile and propionamide result. Of these, only acetonitrile may be treated as a functional parent hydride. 

Nitration of hydroxypropiophenone (7-1) followed by conversion of the phenol to its methyl ether by means of methyl iodide provides the intermediate (7-2) the nitro group is then reduced to the corresponding amine (7-3) by catalytic reduction. The newly introduced amine is then replaced by a nitrile group by successive conversion to the diazonium salt by means of nitrous acid followed by treatment with cuprous cyanide (7-4). Reaction with aluminum chloride removes the methyl ether to afford the ortho acylphenol (7-5). This is converted to the chromone (7-6) as above by reaction with benzoyl chloride and sodium benzoate. The nitrile is next hydrolyzed to the carboxylic acid (7-7) by means of sulfuric acid. The acid is then converted to its acid chloride by means of thionyl chloride and that treated with 2-(A -piperidyl)ethanol (7-8). There is thus obtained flavoxate (7-9) [8], a muscle relaxant whose name reflects its flavone nucleus. 

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