31 Nitriles
As a class, nitriles are characterized by the presence of the C N (—C≡N) group. However, the term nitrile, when used as a suffix in names of individual compounds, denotes only≡N—i.e.,nitrogen triply bound to a single carbon atom. Nitriles may be viewed formally as being derived either by simultaneous replacement of all three hydrogen atoms of a — C H group by nitrogen or by like replacement of both the =O and —OH portions of a —COOH group. F r o m a chemical viewpoint, nitriles are commonly regarded as derivatives of carboxylic acids, and this relation ship has led to the formation of many trivial names based on those of the corresponding acids. Functional isomers of nitriles represented by the generic formula R—NC (often called "isocyanides") are considered in Chapter 32. 3
Recommended Nomenclature Practice Acyclic mononitriles and dinitriles are preferably named substitutive ly by adding the suffixes nitrile and dinitrile, respectively, to the name of the corresponding hydrocarbon. CH CH CH CH CH CN 3
2
CH
2
2
2
Hexanenitrile
3
NCCH CHCH CH CH2CN
3-Methylheptanedinitrile
CH CH=CHCH CN
3-Pentenenitrile
2
2
3
2
2
Cyclic nitriles are preferably named substitutively by adding the suffixes carbonitrile, dicarbonitrile, tricarbonitrile, etc. to the name of the ring system to which the C N group(s) are attached.
^
^—CN
Cyclohexanecarbonitrile
241
242
NOMENCLATURE OF ORGANIC COMPOUNDS
CN 1,5-Anthracenedicarbonitrile CN This type of name is also used for acyclic polynitriles in which more than two CN groups are attached to the same straight chain. CN NCCH CHCH CH CN 2
2
1,2,4-Butanetricarbonitrile
2
When the nitrile function must be treated as a substituting group, the prefix cyano, denoting —CN, is used.
CN ,6-diazanaphthalene-3-carboxylic
CH CN
I
2
NCCH CCH CH CH CN 2
2
2
3,3-Bis(cyanomethyl)heptanedinitrile
2
CH CN As alternatives, trivial names may be used for nitriles in instances where the corresponding acid has an acceptable trivial name (see Chapter 16). Such names are formed by changing the ending ic acid or oic acid to onitrile — e.g., acetonitrile for C H C N and succinonitrile for N C C H C H C N . Names such as succinonitrile imply that all COOH groups have been changed to CN groups. Acyl cyanides corresponding to the generic formula RCOCN are often named analogously to acyl halides (see Chapter 17),—e.g., hexanoyl cyanide for C H C H C H C H C H C O C N - b u t substitutive names-*.g., 2-oxoheptanenitrile—are to be preferred. 2
3
2
3
3
2
2
2
2
Discussion As with other functional classes, conjunctive names (see Chapter 9) are used by Chemical Abstracts for acyclic nitriles in which CN groups are separated from a ring system by one or more carbon atoms— e.g.,
31. Nitriles
243
4-morpholineacetonitrile—but substitutive names are generally to be preferred. Also, reflecting widespread usage, Chemical Abstracts has used the short form propionitrile for C H C H C N rather than propiononitrile. Radicofunctional names for nitriles (see Chapter 9), such as methyl cyanide for C H C N , have appeared frequently in the literature, but these should no longer be employed. The long-known simplest nitrile, HCN, is commonly called hydrogen cyanide. The name "hydrocyanic acid" for HCN, although also widely used, is not recommended. In deference to usage, the trivial name cyanogen for NCCN is acceptable; this compound has seldom been named as a nitrile. Trivial names for amino-substituted nitriles should not be formed by combining the suffix nitrile with the trivial name of the corresponding amino acid, as in "alaninenitrile" or "alaninonitrile." Although Chemical Abstracts formerly made a single exception in the case of "glycinonitrile" (for H N C H C N ) , this name is now cross-referred to aminoacetonitrile. Hydroxy-substituted nitriles, often named as "cyanohydrins", should be given systematic names; cyanohydrin names should be abandoned (see Examples 14 and 15 in Table 31.1). The prefix nitrilo, which would logically denote the substituent =N (by analogy with amino for —NH and imino for =NH), has not been much used with this meaning; usage has been heavily in favor of cyano (for —C=N), as recommended above. However, nitrilo is officially recognized and used as the name of the multivalent substituting group in which nitrogen is singly bound to each of three discrete groups (see Chapter 11). 3
2
3
2
2
2
Table 31.1. Examples of Acceptable Usage
1.
HCN
2.
CH CH CN
3.
CH
3
Methanenitrile Formonitrile Hydrogen cyanide 2
Propanenitrile Propiononitrile* Propionitrile (Chemical Abstracts) 3 -Methy lbu tanenitrile Isovaleronitrile
3
CH CHCH CN 3
4.
2
CH =CHCN 2
Propenenitrile Acrylonitrile
244
NOMENCLATURE OF ORGANIC COMPOUNDS
5.
NCCN
Ethanedinitrile Oxalonitrile Cyanogen
6.
NCCH CH CH CH CN
Hexanedinitrile Adiponitrile
7.
C H CN
Benzenecarbonitrile Benzonitrile
8.
C H CH CN
2
6
6
2
2
S
S
Phenylethanenitrile Phenylacetonitrile
2
NC -
10.
2
0
-
Azabenzene-3,5 -dicarbonitrile 3,5-Pyridinedicarbonitrile
™
3-Cyanopropanoic acid 3-Cyanopropionic acid
NCCH CH COOH 2
2
CN 11.
NCCH CHCH CN 2
1,2,3-Propane tricarbonitrile
2
12. CH CH CN 2
2
2-( 2-Cy anoethy 1)-1,4-cyclohexanedicarbonitrile
CN
13.
NCCH CHCN 2
I NH
14.
2
HOCH CH CN 2
2
2-Aminobutanedinitrile 2-Aminosuccinonitrile not Aspartonitrile
3-Hydroxypropanenitrile 3-Hydroxypropiononitrile not Ethylene cyanohydrin
J
245
31. Nitriles 15.
CH I CH CCN I 3
3
16.
C H COCN 6
s
2-Hydroxy-2-methylpropanenitrile 2-Hy droxy-2-methy lpropiononitrile* not Acetone cyanohydrin
Oxophenylethanenitrile Benzoyl cyanide
"Recommended in 1965 IUPAC Rules. See Discussion Section.
