Determination of Organic Functional Groups by Chemical Means SIDNEY SIGGIA General Aniline & Film Corporation, Easton, Pa. I n order to use a chemical reaction for determining a functional group, a t least one of the reactants or products must be measurable. Reactions t h a t liberate or consume a n acid, base, oxidant, reductant, or gas are particularly adaptable for quantitative analytical purposes. Several reactions which liberate or consume easily determinable compounds such as water can be used to measure functional groups. Reactions t h a t yield precipitates also have analytical possibilities. Equilibrium, incomplete reaction, poor end points, and interferences are t h e troubles usually encountered. Techniques are available for minimizing these difficulties.
B. 2RCHO
T
H E methods available for functional group determination have been amply described and reviewed (16,22). Methods exist for practically all the functional groups, but situations often arise when changes in methods, or sometimes a completely new procedure, are necessary. This paper is concerned with the techniques and reasoning involved in devising a new method of analysis or making changes in known procedures.
+ 2Na2SOa + HzSO,*
2RCHOH
I
+ Na2S04 (21 1
SOsNa ( a ) RCH(0Ri)z
( b ) ROCH=CHz
1+
Hf H20 + (a) RCHO
+ ( a ) 2R10H
(Aldehydes determined as in above equation)
CHEhlISTRY O F F U h C T I O h A L GROUPS
When a new procedure is necessary, the chemistry of the functional group in question must be completely surveyed. The factors involved are: the presence of a t least one reactant or product that can be measured, the completeness of the reaction, and effect of impurities. A reaction in which a base, acid, oxidant, or reductant is liberated or consumed is a good one to use for functional group determination. These materials are very easily measured by common analytical means. In the following examples of known analytical methods which use reactions of this type, the asterisk indicates the component determined.
-----f
+ ( b ) ROH (14:
( b ) CH~CHO
C. Titration of basic materials such as amines (primary, secondary, tertiary), pyridine, quinoline, carboxylic acid salts, etc., with standard acid solutions. (Where water gives unsatisfactory results because of insolubility or poor end point, a mixture of 1 to 1 ethylene glycol and isopropyl alcohol can bezused, 11).
Acid Consumed Acid Produced
A.
(a)
CHSC
\
\
NHz
(b) /
~
RC=S
CH3C XO
c1
+ 3,.i(S02)2'C6H3CNO* fHC1* (8) O 'H
( c ) Some RNHRl
0
I
e
B. ( a ) R R1 (RI could = H )
No
( a ) CHsC
+ H2O
( b ) RCH(OR,)z
O 'R 0
/I
( b ) RSHC-CH,
+
(c) ROCH=CHz
CHjCOOH* (10)
+ H2O
0%
(c) R-X-RI
1 I
L o
i d ) R-C-R1
~
OR?
CH,
378
+ H20
~
i1
+
"20H.HC1
-
V O L U M E 22, N O . 3, M A R C H 1950
379
SOH
ll
(a)RCRi
Oxidant Produced. Iodine liberated from iodides by peroxidrb is measured (not applicable to all organic peroxides) ( 5 ) .
+ HzO + HC1*
Reductant Consumed A. TiCl3 reductions of --SO?, -NHNH-, -N=N-, and diazonium salts (TiCl,* is measured) ( 2 , 15). B. As203 consumed on reaction with peroxides is measured
KOH
II
+ 2RiOH + H20 + HCl*
( b ) RCH
(13).
$;OH 1
( c ) CH&H
Reactions in which a gas is liberated or consumed can also be used for quantitative determination of functional groups. .4 liberated gas can be collected and measured-i.e., the nitrogen liberated on decomposition in the determination of diazonium compounds and hydrazines.
+ ROH + H20 + HCl*
KOH
+ RlOH + RzOH + H
