Time Figure 1 . Gas chromatogram of trimethylorthoformate (TMOF)
Effects of Raw Material Change in Manufacturing Process Resolved Current shortages of many chemicals present a new challenge to the analytical chemist. Product quality in many industrial processes requires complete knowledge of compositions of chemical intermediates, including type and concentration of trace impurities. Active species may seriously affect product yield as well as product quality. This problem becomes acute when a plant finds it necessary to change the source of supply of a raw material, because maintenance of production requires rapid assessment of the nature of process stream impurities. A special emergency task force may be necessary to bring together the analytical expertise vital in resolving the effects of a raw material change on the manufacturing process. A plant faced such a problem in looking for another source of trimethylorthoformate used in a complex manufacturing process. Identification and determination of low levels of impurities were essential, requiring a multitechnique approach. Complete analysis required gas chromatography, infrared and ultraviolet spectrometry, nuclear magnetic resonance, mass spectrometry, distillation, and chemical methods. Preliminary GC studies (Figure 1) indicated at least eight impurities. As indicated in Figure 2, GC/MS served to identify GC peaks 1, 2, and 3 as methyl formate, 2-methoxyethanol, and methanol, respectively. Compo-
John Mitchell, Jr. E. I. du Pont de Nemours and Co. Plastics Department Experimental Station Wilmington, Del. 19898
Table I. Analytical Data on GC Peak No. 7 IR (cut collected in CCI4) Absorption band, cm _1
~1720 ~1625 ~108f>
Group
>C=0 0 = C — C = C or C=C—C=C C—O—C
NMR (multiple collection in CDCIS and time averaging, 50X) Chemical shift, ppm (re TMS as external std.) Group ~3.8 ~5.6 —9.5 UV (cut collected in CH 3 OH) Absorption max
—OCH, — C H = C H — (trans) 0=CH Group
Î 240 nm MS m/e = 86 (apparent parent mass)
804 A · ANALYTICAL CHEMISTRY, VOL. 46, NO. 9, AUGUST 1974
=CHCH—
The Analytical Approach Edited by Claude A. Lucchesi GC (Peak No.) HCOOCH3
1 GC/MS
2
CH 3 OCH 2 CH 2 0H
3
CH,OH
4
CCI4 solution
m
5
CCI4 solution
IR
CDCI3 solution
Ν MR
CHCI,
CH3CH20(OCH3)2CH
MS
6
CCI4 solution
IR
CH3OH solution
UV
CgHs'Ch^
7 8
(See Table I) IR
CCI4 solution
CH3OCH2OCH2OCH = CHCH3 MS
Figure 2. Identification of components separated by gas chromatography nent 4 was identified as chloroform with the aid of IR. Fractions repre senting component 5 were collected in CCI4 and in CDCI3 for IR and NMR studies and MS was obtained directly. The spectra indicated ethyl dimethylorthoformate. Component 6 was iden tified as toluene. From GC, MS, and IR data, component 8 was identified as methoxymethoxymethyl-1-propenyl ether. Component 7 proved to be the most challenging. Collection of analytical information is shown in Table I. In frared spectra indicated C = 0 groups, conjugated unsaturation, and ether groups. NMR (with time averaging) showed methoxy, unsaturated methy lene, and aldehyde group protons. Mass spectrometry indicated a molec ular ion of 86; ultraviolet, an unsatu rated aldehyde. The 2,4-dinitrophenylhydrazone (2,4-D) derivative, pre cipitated from ethyl alcohol solution, had a molecular weight of about 432 (Table II). It was orange in color and decomposed on heating, indicative of a dialdehyde. Elemental analysis of the 2,4-D supported the compound malondialdehyde. However, the data were inconsistent with direct results by IR, NMR, UV, and MS. Repeat of the di rect analyses of the GC fractions veri fied the original results, including a methoxyl group. The suggested struc ture was C 4 H 6 0 2 (MW = 86), C H 3 O C H = C H C H O (3-methoxyacrolein). Formation of the di-2,4-D-deriv-
ative could be explained from cleavage of the methoxyl group in the strongly acid reagent to form the enol. The enol, in turn, would be expected to rearrange to the dialdehyde as the de rivative was formed: H2S04
CH3OCH=CHCHO
Table II. 2,4-Dinitrophenylhydrazone (2,4-D) of GC Peak No. 7 MS gave m/c = 432
Elemental analysis (all direct d e t e r m i nations)
»
(Apparent molecular ion) C = 41.9% H = 2.9 0 = 30.5 Ν = 25.8
H20
HOCH=CHCHO
2 4 D
' " >
reagent
101.1 A s s u m i n g di- derivative = MW of a di c a r b o n y l c o m p o u n d = 72 (432 392 + 32) = C,H.,0. * 0 - € H — C H — H C -0
OCHCH 2 CHO —>• 2 , 4 - D In summary, the eight compounds shown in Table III were identified. They are arranged in order of elution from the GC column. In conclusion, the progressive ana lytical group associated with an indus trial research organization combines expertise with versatility. Emphasis is on problem solving by the most effi cient and effective means. Specificity is all important in detecting sub stances in concentrations varying from ppb to major amounts. The analytical chemist is presented with the chal lenge of contributing to special chemi cal structure needs in research, pro duction, and marketing. This chal lenge is now all the more exciting as we must provide reliable results with respect to EPA, OSHA, and FDA re quirements.
Table III. Impurities Found in Trimethylorthoformate Methyl formate 2-Methoxyethanol Methanol Chloroform
HCOOCH 3 CHsOCHiiCHaOH CH 3 OH CHCI;, OCH 3
Ethyl d i m e t h y l -
CH3CH.OCH
ui i i i u i u i ι ιΐα ie
Toluene 3-Methoxyacrolein Methoxymethoxymethyl-1p r o p e n y l ether
/
OCH 3 C 6 H,,CH 3 CHsOCH-^CHCHO CH3CH--CHOCH2OCH 2 OCH 3
A N A L Y T I C A L CHEMISTRY, VOL. 46, NO. 9, AUGUST 1974 · 805 A
