Aldehydes

20

Downloaded by SUNY STONY BROOK on December 17, 2014 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0126.ch020

Aldehydes

Compounds containing the carbonyl group (>C=O) attached only to carbon or hydrogen have been divided traditionally into two function al classes called aldehydes and ketones. This distinction has been made because of certain characteristic differences in the reactivity of the C=O group depending upon whether or not it is attached to hydrogen. Thus, aldehydes are carbonyl compounds containing one or more —CH=O groups (commonly written C H O ) , and ketones (see Chapter 29) are carbonyl compounds in which the C=O group is attached to two carbon atoms. Thioaldehydes contain the —CH=S group (commonly written CHS). Some oxygen and sulfur derivatives of aldehydes are also treated in this chapter. These include the acetals and hemiacetals, which contain the groups — C H ( O R ) and —CH(OH)(OR), respectively, and their analogs in which one or more oxygen atoms have been replaced by sulfur. Nitrogen derivatives o f aldehydes, such as oximes and hydrazones, are discussed in Chapter 32. 2

Recommended Nomenclature Practice Acyclic monoaldehydes are named substitutively by adding the suffix al to the name o f the corresponding hydrocarbon, the final e of the hydrocarbon name being elided. CH eH CH CH CH CHO

Hexanal

CH =CHCH CH CHO

4-Pentenai

3

2

2

2

2

2

2

2

Acyclic dialdehydes are named similarly by using the suffix dial but retaining the final e o f the hydrocarbon name. OHCCH CH CH CH CH CHO 2

2

2

2

Heptanedial

2

Acyclic polyaldehydes in which more than two C H O groups are attached to the same straight chain are named substitutively by using the suffixes tricarbaldehyde, tetracarbaldehyde, etc. with the name of the chain. 160 In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

161

20. Aldehydes OHCCH CHCH CHO 2

2

1,2,3-Propanetriearbaldehyde CHO Cyclic aldehydes in which one or more C H O groups are attached to a ring system are named substitutively by adding the suffixes carbaldehyde, dicarbaldehyde, tricarbaldebyde, etc. to the name o f the ring system.


2-Anthracenecarbaldehyde

CHO 2,6-Naphthalenedicarbaldehy de

OHC

When all o f the C H O groups in a polyaldehyde cannot be treated as recommended above or when another functional group standing higher in the Order o f Precedence o f Functions (Table 8.1) is present, the terms methanoyl, dimethanoyl, trimethanoyl, etc. (or the more familiar formyl, diformyl, triformyl, etc.) are used as prefix names. CH CH CH CHO 2

2

2

4-(Methanoylmethyl)octanedial OHCCH CHCH CH CHO 2

2

2

NH CO—f^^^^l—CHO II I NH C O — ^ s ^ A s ^ ^ 2

C

H

6,7-Dimethanoyl-2,3-naphthalenedicarboxamide

O

2

Trivial names for the more common aldehydes based on trivial names of the corresponding carboxylic acids (see Chapter 16) have been used widely. Such names are formed by changing the suffix ic acid or oic acid to aldehyde, as in acetaldehyde for C H C H O and benzaldehyde for C H C H O . When polyaldehydes are named in this manner, it is implied that all the C O O H groups have been converted to C H O groups—e.g., succinaldehyde for O H C C H C H C H O . Some acceptable trivial names of aldehydes are included in Table 20.1. Thioaldehydes are named analogously to aldehydes by using the suffixes thiol and carbothialdehyde in place of al and carbaldehyde; the term methanethioyl (or the more familiar thioformyl) is the prefix name for the C H S group. F o r typical names o f thioaldehydes see Examples 22-24 in Table 20.1. 3

6

5

2

2

In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

162

NOMENCLATURE OF ORGANIC COMPOUNDS

Acetals are preferably named systematically as ethers—e.g., 1,1-dimethoxyethane for C H C H ( O C H ) —and hemiacetals as alcohols—e.g., 1-methoxyethanol for C H C H ( O H ) ( O C H ) . Thioacetals and thiohemiacetals containing one or more sulfur atoms are named as thioethers and thiols or alcohols, respectively; cyclic structures are treated as heterocyclic systems (see Examples 27-30). 3

3

2

3

3


Discussion Although, as pointed out above, the functional distinction between aldehydes and ketones is firmly established in the chemical literature, its value in systematic nomenclature is open to question. Structurally, aldehydes bear the same relationship to ketones as do primary alcohols to secondary alcohols and could be named using the suffix 1-one rather than al,—e.g., 1-propanone for C H C H C H O . Indeed, Chemical Abstracts uses this approach in forming parent names for certain ketones having a ring system directly attached to the carbonyl group—e.g., 1-cyclohexyl1-butanone for C H C O C H C H C H . However, the 1-one type of nomenclature has not as yet been officially recognized or used for aldehydes. Although the identity of the aldehyde function is customarily preserved by use of the suffixes al and carbaldehyde, as recommended above, the situation is different when the C H O group is named as a prefix. For a substituting C H O group attached to a chain, either methanoyl (or formyl) or oxo (denoting = 0 only) may be used as a prefix, according to the 1965 I U P A C Rules—e.g., 4-methanoylbutanoic acid or 5-oxopentanoic acid for O H C C H C H C H C O O H . The former alternative is the choice of Chemical Abstracts and seems preferable since it maintains the identity of the aldehyde function. (The prefix oxo does not, of course, distinguish between an aldehyde group and a ketone group.) However, if aldehyde and ketone groups are both to be named as substituents on the same chain, use of oxo for both types of group is recommended,—e.g., 3,5-dioxopentanoic acid for O H C C H C O C H C O O H . The IUPAC-recommended suffix carbaldehyde for C H O has not yet found extensive use; Chemical Abstracts still uses the older form, carboxaldehyde. However, carbaldehyde is recommended here because strictly speaking both the ox and aldehyde portions of carboxaldehyde denote an oxygen atom, resulting in unnecessary and possibly misleading redund ancy. Acyclic aldehydes in which C H O groups are separated from a ring system by one or more carbon atoms are given conjunctive names (see Chapter 9) in many instances by Chemical Abstracts, e.g., 2-pyridinepropionaldehyde for 3-(2-pyridyl)propionaldehyde, but substitutive names are preferred for general use. Trivial names for aldehydes based on those trivial names of carboxylic acids listed as acceptable in Chapter 16 are, of course, implicitly 3

6

2

1 1

2

2

2

2

3

2

2

2


163


20. Aldehydes

acceptable themselves. However, except for these, and a few other very common trivial names included in Table 20.1, trivial names of aldehydes should be abandoned in favor of systematic names. In forming acid-derived trivial names for aldehydes, two points warrant emphasis: the acid name must be trivial, not systematic,, and both the ending ic and the word acid are replaced by the suffix aldehyde. Thus, names such as "ethanaldehyde" for acetaldehyde and "oleic aldehyde" for olealdehyde are incorrect and should not be used. Also, radicofunctional names such as "w-octyl aldehyde," which have found some use, should be abandoned. Trivial aldehydic acid names such as malonaldehydic acid for O H C C H C O O H are recognized in the 1965 I U P A C Rules and until 1972 were used by Chemical Abstracts, but the corresponding systematic names are to be preferred. The prefix thio should not be used in naming individual thioalde hydes, as in "thioformaldehyde, " "thiobenzaldehyde," and the like. A s in other classes of compounds the use of thio to denote replacement of oxygen by sulfur can often lead to ambiguous names. The class name thioaldehyde is, of course, acceptable, as are the class names monothioacetal, dithioacetal, monothiohemiacetal, and dithiohemiacetal. Such older names for acetals as acetaldehyde diethyl acetal for C H C H ( O C H ) are recognized in the 1965 I U P A C Rules, but ethertype systematic names are preferred. The trivial names methylal for H C ( O C H ) and acetal for C H C H ( O C H C H ) should no longer be used. 2

3

2

2

3

5

2

2

3

2

3

2

Table 20.1 Examples of Acceptable Usage l.

HCHO

Methanal Formaldehyde

2.

CH CHO

Ethanal Acetaldehyde

3.

CH CH CHO

Propanal Prop ionaldehy de

4.

CH CH CH CHO

Butanal Butyraldehyde

CH CHCHO

2-Methylpropanal I sobu ty raldehy de

5.

3

3

3

2

2

3

CH

6.

2

3

CH CH CH CH CHO 3

2

2

2

Pentanal Valeraldehyde


164 7.

NOMENCLATURE OF ORGANIC COMPOUNDS

CH CHCH CHO 3

CH

3

CH CH CH CH CH CHO

Hexanal

Cl CCHO

Trichloroethanai Trichloroacetaldehyde Chloral

CH =CHCHO

Propenal Acrylaldehyde Acrolein

11.

OHCCHO

Ethanedial Oxalaldehyde Glyoxal

12.

OHCCH CHO

13.

OHCCH CH CH CH CHO

Hexanedial Adipaldehyde

14.

C H CHO

Benzenecarbaldehyde Benzaldehyde

8.

9.


3-Methylbutanal I sovaleraldehy de

2

10.

3

2

2

2

2

3

2

Propanedial Malonaldehyde

2

2

6

5

2

2

2

4-Methylbenzenecarbaldehyde p-Tolualdehyde

Cyclohexanecarbaldehyde

1,2-Benzenedicarbaldehyde Phthalaldehyde

Methanetricarbaldehyde

Oxacyclopenta-2,4-diene-2-carbaldehyde 2-Furancarb aldehyde 2-Furaldehyde Furfural


20. Aldehydes


20. OHCCH

2

-O

21.

OHC—^

22.

CH CH CHS 3

CH CHO 2

4-Methanoylbenzenecarboxylic acid 4-Formylbenzoic acid

^—COOH

Propanethial not Thiopropionaldehyde

2

-CHS

23.

1,2-Benzenedicarbothialdehyde not Dithiophthalaldehyde

-CHS

3-Methanethioylpropanoic acid 3-(Thioformyl)propionic acid not 4-Thiosuccinaldehydic acid

24.

SHCCH CH COOH

25.

CH CH CH CH(OCH )

26.

CH OCHCH CH CHOCH I I OH OH

27.

CH CH CH(SCH CH )

2g

CH CH CH CHSCH

2

3

2

2

2

3

3

2

3

3

2

2

3

3

1,1-Dimethoxy butane

2

2

2

2

1,4-Phenylenediethanal 1,4-Benzenediacetaldehyde

2

3

l,4-Dimethoxy-l,4-butanediol

1, l-Bis(ethylthio)propane

l-(Methylthio)-l-butanethiol

SH

CH CH CHSCH CH 3

29.

30.

2

2

3

l-(Ethylthio)-l-propanol OH

f^^CH

2-Methyl-l-oxa-3-thiacyclopentane 3


Aldehydes

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