Composition Characterization of Fatty Acid Zinc Salts by Chromatographic and NMR Spectroscopic Analyses on Their Fatty Acid Methyl Esters

Table 2

Optimized conditions for preparation of FAMEs from zinc stearate^a by acid-catalyzed esterification using the conc. HCl/methanol/toluene method.

Rxn no.	Temp (°C)	Time (min)	Amount of conc. HCl	Yield^c (%)	Conversion (%)
					By NMR	By GC-MS^e
						C16^e	C18^e
1	90	60	2 g (5 eq^b)	94.1	>99	100.0 ± 3.4	100.0 ± 6.6
2	90	30	2 g (5 eq)	93.8	>99	110.9 ± 1.4	113.1 ± 3.0
3	90	10	2 g (5 eq)	94.6	>99	103.4 ± 3.8	105.7 ± 4.7
4	90	10	0.8 g (2 eq)	96.3	>99	107.3 ± 1.2	104.9 ± 0.5
5	90	10	0.4 g (1 eq)	94.9	91	92.2 ± 3.9	96.3 ± 7.0
6	90	60	0.2 g (0.5 eq)	—	Insoluble^d	—	—
7	45	30	2 g (5 eq)	93.4	>97	102.3 ± 1.3	103.8 ± 2.3
8	45	30	0.8 g (2 eq)	96.1	>97	106.6 ± 1.3	103.4 ± 2.5
9	45	10	2 g (5 eq)	91.7	>97	100.7 ± 0.8	101.5 ± 0.4
10	45	30	0.4 g (1 eq)	94.4	77	78.8 ± 2.6	78.5 ± 2.7
11	45	30	0.2 g (0.5 eq)	—	Insoluble^d	—	—
12	rt	30	2 g (5 eq)	91.9%	73%	78.8 ± 0.9	77.6 ± 0.8

^a,eZinc stearate consisted of C16 and C18 fatty acid zinc salts as major components and small amounts (less than 3%) of C14 and C20 fatty acid zinc salts. ^bEquivalent number was calculated as mole of HCl per mole of zinc stearate. ^cYield was calculated based on weight measurements. ^dReaction mixture remained insoluble throughout the reaction. ^eGC-MS data were expressed as means ± standard deviation (n = 3).