Removal of Alcohols from Complex Mixtures During Gas Chromatography SIR: After a hydroboration reaction mixture was analyzed by gas chromatography, subsequent analysis on this column of our neutral fraction revealed that we did not obtain our expected gas chromatographic pattern. The peaks corresponding to the alcohols were completely missing. Knowing that primary and secondary alcohols will react with boric acid ( I ) , we theorized that the boric acid present in the hydroboration misture had removed the alcohols. To prove this assumption, the last 6 inches of the gas chromatographic column were replaced with a section to which 1% boric acid had been added to the already-coated packing material. This was done by mi\ing powdered boric acid a i t h the 20% Carbowas 20hI on 60- to 80-mesh Chromosorb P in petroleum ether and evaporating the petroleum ether in a rotating vacuum evaporator. The main column to which the boric acid section was attached was 1, 4-inch X 4 l '2-foot column packed with 20% Carbowas 2011 on 60- to 80-mesh Chromosorb P. The columns were heated overnight a t 225" C. prior to use. Boric acid will lose water on heating to form metaboric acid, pyroboric acid,
or the anhydride, depending on the temperature. Analysis of the neutral fraction on this combination column showed that the alcohols had been removed. To determine the classes of compounds that are removed by boric acid, a mixture containing primary, secondary, and tertiary alcohols and nonalcohols listed in Table I was prepared and gas chromatographed. An F & 11 Model 720 dual column gas chromatograph was used. ;ishort column approaimately 6 inches long which contained 3% of added boric acid was attached to the end of column B just ahead of the detector block. The recorder pen was positioned on the center of the chart paper and the mixture listed in Table I was injected simultaneously into columns *I and B. Materials emerging from column A were detected by upscale deflections, while materials emerging from the boric acid-treated column B were detected by downscale deflection. The retention times were slightly longer for materials eluted from column B , which prevented the response signals from cancelling each other. The chromatogram is shown in Figure 1.
Table I. Known Mixture SonDesig- Weight, Alcohols alcohols nation g. tert-Butyl 1 0.5 2 0.5 n-Butyl A 0.75 p-Cymene Linalool 3 1.0 4 1. o Menthol Menthyl B 1.0 phenylacetate 5 1.0 Benzyl 2-Acetyl C 1 .o pyrrole
Peak 3, which corresponded in retrntion time to linalool, was not retained by boric acid. The material with this retention time was collected, and its infrared spectrum was determined. Results indicated that a mixture of myrcene, a dehydration product of linalool, and water was present. The water was probably condensed from the atmosphere during the trapping.
PEPPERMINT OIL
14
0
5
IO
15
Minuter
I
IO
15
5
Figure 1 .
Minutes Gas chromatogram of mixture listed in Table I
1 0-ft. X '/4 in. 2070 C a r b o w a x 20M Same as A plus 6-in. X '/
