Gas chromatography and mass spectrometry of
bis(alkylamino)-s-triazines
Citation for published version (APA):
Leclercq, P. A., & Pacakova, V. (1979). Gas chromatography and mass spectrometry of bis(alkylamino)-s-triazines. Journal of Chromatography, A, 178(1), 193-207. https://doi.org/10.1016/S0021-9673(00)89708-3
DOI:
10.1016/S0021-9673(00)89708-3
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CHROM. 12,071
GAS CHROMATOGRAPHY AND MASS SPECTROMETRY OF BIS(ALKYL-
AMINO)-s-TRIAZINES P. A. LECLERCQ
Laboratory of Instrumental Analysis, Eindhoven University of Technology, P-0. Box 513, 5600 MB Eindhoven (The Netherlands)
and
V. PACAKOVA
Department of Analytical Chemistry, FacuIty of- Sciences, ChrIes University, AIbertov 2030, 12840
Prague 2 (Czechoslovakia) .-
(Received May 31st, 1979)
SUMMARY ‘.
The retention behaviour of 22 2-chloro, 2-methoxy- and 2-methylthio4,6- bis(alkylamino)triazines was studied on four gas chromatographic columns with different polarities. The most polar stationary phase, Carbowax 20M, was found to be the best suited for the separation of these compounds. The differences in the retention indices of the same triazines on columns with different polarities were found to be proportional to the pK, values and the dipole moments of these compounds.
Electron-impact mass spectra and deduced fragmentation schemes are given. The stability of the compounds under electron impact increases in the order chloro < methoxy < methylthio derivatives_
Chemical-ionization mass spectra, using methane as reagent gas, are tabu- lated. It has been found that the ease of fragmentation of the protonated molecular ions of chlorotriazines is related to the low proton affinity of the leaving neutral HCl group. In the isobutane chemical-ionization mass spectra all triazines exhibited the protonated molecular ion as the base peak with only relatively minor fragmentations.
INTRODUCI’ION
s-Triazine derivatives are important compounds in agriculture and industry because of their herbicidal properties. These compounds are 1,3,5triazipes substi- tuted in positions 2, 4 and 6. Most properties of the s-triazine derivatives are deter- mined by the substituents; the ring itself is not involved except for its effect on the charge distribution.
The character of s-triazines is determined primarily by the substitltent in posi- tion 2, commonly chlorine (the commercial name ends with -azine), metboxy (ending in -tone) or thiomethyl (ending in -tryne). Positions 4 and 6 are usually substituted by various alkylamino groups.
194 P. .A. LECLERCQ, V. PACAKOVA The physico-chemical properties of s-triazines are very variable, even within the restricted group Gf the commercially available derivatives. The striazines are weak bases, their pK,, values rangin, = from 1.65 for simazine to 4.46 for terbutone. The dissociation constant is strGngIy affected by the substituent in position 2. The basicity increases in the order Cl < SCH, < OCH,. The groups in positions 4 and 6 have smaller but still pronounced effects on the basicity of s-triazines: the greater the num- ber of ethyl groups ‘in place of hydrogen atoms, the more basic are the compounds.
Different properties of s-triazines are reflected in both their biological and chromatographic behaviour. The availability of a wide range of derivatives offers a great opportunity to study extensively the relationships between the structure and the chromatographic, spectrometric, electrochemical and mass spectrometric be- haviour.
Gas chromatography has become the prevailing method for the analysis of s-triazines1-‘8. Most of the papers published to date deal with the application of gas chromatography for the determination of residues in soil, grain, etc.3*4*6-8*11-1J. In this work the gas chromatographic and mass spectrometric behaviour of s-triazine derivatives has been studied and the structural correlations are discussed_
EXPERIMENTAL
All s-triazines studied were products of Ciba-Geigy (Basle, Switzerland) and are listed in Table I.
The following stationary phases and column packings for gas chromato- graphy were used: XE-60 (Applied Science Labs., State College, Pa., U.S.A.); SE-30 and Carbowax 20M (Carlo Erba, Milan, Italy): Reoplex 400 and Versamid 900 (Hew- lett-Packard, Avondale, Pa., U.S.A.): Chromaton N-AW, 60-50 mesh (Lachema, Brno, Czechoslovakia); Chromosorb W, silanized, 60-80 mesh (Carlo Erba).
Other chemicals used included the following: CZZ-C,s n-alkanes (Applied Science Labs.): sodium hydroxide, p-a., without glycerol (Lachema); perchloric acid, p-a_, 70 % (Carlo Erba); buffers pH 4.00 and pH 7.02 (Radiometer, Copenhagen, Den- mark)_
As reagent gases for Chemical-iGniZatiGn mass spectrometry, methane of 99.995”,6 purity (code N45) and isobutane of 99.95% purity (code CH35) were obtained from L’Air Liquide (Liege, Belgium).
For pH measurements a PHM 64 pH meter (Radiometer) was employed. Gas ci~ronzatograpiz~
The measurements were carried out on a Hewlett-Packard (Palo Alto, Calif., U.S.A.) Model 5700 gas chromatograph equipped with a Aame-ionization detector_ Stainless-steel columns (140 cm x 3 mm I.D.) were used.
Column A was packed with 37/, Carbowax 20M on Chromosorb W, column B with 5 y/, XE-60 on Chromaton N-AW, column C with 5 T< Versamid 900 on Chro- mosorb W, and column D \vith 5 T/i SE-30 +- 2 76 Reoplex 400 on Chromosorb W.
Nitrogen was used as the carrier gas at a flow-rate of 40 ml/min. Columns E, C and D were operated isothermally at 195” and column A at 215”. The injection block temperature was maintained at 230”. The detector temperature was 210” (column B, C and D) and 230” (column A).
TABLE I
COMPOUNDS STUDIED
(a) Di(monoalkyiamino) derivatives (RL = R; = H) No. Trivial name
-1 - - 2 - 3 Propazine 4 Terbutylazine 5 Atrazine 6 Norazine 7 Simazine 8 Prometone 9 Terbutone 10 Atratone 11 Noratone 12 Simetone 13 Prornetryne I4 Terbutryne 15 Ametryne 16 Desmetryne 17 Simetryne 18 Metoprotxyne RI RZ R3 ~_ -_ ____-__ Cl H tert_-Bu Cl tert.-Bu tert.-Bu
:t Et i-Pr i-R Ierr.-Bu
Cl Et i-Pr
Cl Me i-Pr
Cl Et Et
OMe i-Pr i-Pr
OMe Et tert.-Bu
OMe Et i-Pr
OMe Me i-Pr
OMe Et Et
SMe i-Pr i-Pr
SMe Et tert_-Bu
SMe Et i-pr
SMe Me i-Pr
SMe Et
SMe EHI),OMe i-Pr
_ -.- (b) Diethylamino and sec.-batylamino derivatives
No. Trivial name RI R2 & R3 K
19 Ipazine 20 Trietazine 21 Chlorazine 22 sec.-Bumetone Cl Cl Cl OMe i-Pr Et Et Et H H Et H Et Et Et sec.-Bu Et Et Et H UV spectrophotometr)
For the measurement of dissociation constants the procedure of Albert and Serjeantf9 was adopted. The measurements were carried out on a Specord UV VIS spectrophotometer (Carl Zeiss, Jena, G-D-R.).
Mass spectrometry
Electron-impact (EI) mass spectra were obtained on an AEI MS-12 single- focusing magnetic sector instrument (AEI, Manchester, Great Britain) under the following conditions: electron ener,y, 70 eV; electron current, 0.50 mA; ion accelera- ting voltage, 4 kV; scan time, 2 set per decade; source temperature, 250”.
Chemical-ionization (CI) mass spectra were produced with a Model 4000 (Finnigan, Sunnyvale, Calif., U.S.A.) quadrupole instrument under the following
196 P. A. LECLERCQ, V. PACAKOVh TABLE II
p&C,, VALUES AND RETENTION INDICES (I) ON FOUR STATIONARY PHASES
A = Carbowax 20M (215’); B = XE-60: C = Versamid 900; D = SE-30 -+- Reoplex 400 (5:2). Columns B, C and D were operated at 195’. __.._~. _. _____
__- ___~.
No. ThiaI name Mol. wt. PK* ZA 43 Lz ZD
_~_~_~.__~. ~~ _ -____ _.. ___. ..____~.___ _I___ 1 - 901.5 - 2336 - - 1766 19 Ipazine 243.6 i.99= 246 1 2378 2141 1907 2 - 257.8 - 2501 2418 2185 1938 21 Chlorazine 257.8 1.74 2309 2286 1935 1791 20 Trietazine 229.7 1.88 2557 2415 2196 1932 3 Propazine 119.7 1.85 2633 2462 2262 1973 4 Terbutylazine 229.7 1.94” 2664 2504 2285 1999 5 Atrazine 115.7 1.68 2722 2509 2318 2023 6 Norazine 201.5 l-88= 2761 2518 2320 2029 7 Simazine ‘01.5 1.65 2806 2553 2375 2075 8 Prometone 225.3 4.28 2539 2350 2199 1916 9 Terbutone 225.3 4.46” 2570 2396 2205 1938 22 sec.-Bumetone 725.3 4.23” 2676 2470 2302 2015 10 Atratone 211.3 4.20 2610 2418 2212 1972 11 Noratone 197.1 4.15 2620 2411 2204 1966 12 Simetone 197.’ 4.17 2680 243s 2270 1990 1s Prometrjme 241.3 4.05 2758 2558 2378 2099 14 Terbutrvne 241.3 4.38” 2793 2608 7403 7122 15 Ametryne X7-3 4.00 2837 ‘610 2418 ‘139 16 Desmetryne 213.3 3.9’2’ 2565 2623 2452 1141 17 Simetryne 213.3 4.00” 2915 2656 2465 2185 I8 Metoprotryne 271.4 3-98”’ 3202 2983 2726 2457 _~_~~
* Values from ref. 21, except where indicated othenvise from ref. 22.
conditions: electron energy, 25-40 eV; electron current, 0.20 mA; scan time, 1 set per scan; source temperature, 250” (methane) and’ lSOc (isobutane). The ion source pressure was maintained at 0.15 Torr gauge reading..
Samples Lvere always introduced through a direct introduction probe and heat- ed to 250’. The spectra given were obtained at probe temperatures of 40-120’.
RESULTS AND DISCUSSION
The retention indices (I) on four stationary phases were measured (Table 11). Some of the results has been already publishedt6. The polarity of the stationary phases used is given by the McReynolds constantGo. The most polar stationary phase, Carbowax LOM (Z1= 2308), is best suited for the separation of triazines. The other three liquid stationary phases, XE-60 (r1= 1785), Versamid 900 (n = 969) and the mixed phase SE-30 f Reoplex 400 (5 :2) (.Z1= 940), can also be used for the analysis of s-triazines.
The chromatographic data depend primarily on the nature of the substituent in position 2. The order of elution is first methoxy, then chloro and finally thiomethyl derivatives_ In a series of s-triazines with the same substituent in position 2, the retention order is chiefly influenced by the spatial shielding of the substituted NH
groups in positions 4 and 6 (see Table II). The weakest shielding, causing the longest retention, is exerted by the ethyl group, the strongest by the terr.-butyl group and isopropyl lies in between.
The retention data for the s-triazines are influenced by their basic character_ In order to complete the list of pK, data given in the literature”, we measured 22 the dissociation constants of s-triazines by UV spectrophotometry according to Albert and Serjeant19. The results are given in Table II. The differences between Cl, OCH3
and SCH, derivatives can be attributed to the activating mesomeric effect of the methoxy and thiomethyl groups and the deactivating inductive effects of the chlorine atom.
XE-60 seems to be the most suitable liquid stationary phase for structural correlations. The differences in the basicity of the compounds contribute to the higher retention indices of terbutylazine and terbutryne on XE-60 in comparison with atrazine and ametryne, and to their poor separation.
The differences between the retention indices on XE-60 and on the mixed phase SE30/Reoplex 400 can be correlated with pK, values and dipole moments. As can be seen from Table III, the ilIvaIues are proportional to pK,.
TABLE III
COMPARISON OF Jf AND pK,, VALUES
No. Trivial name 43-D
4 ~___ Terbutylazine 505 5 Atrazine 485 7 Simazine 475 14 Terbutryne 486 15 Ametryne 471 17 Simetryne 471 9 Terbutone 456 10 Atratone 446 12 Simetone 445 -____ _~. ___~_~~ ._ PK7 1.94 1.68 1.65 4.38 4.00 4.00 4.46 4.20 4.17
Data on dipole moments are scarce in the literature”. The correlations be- tween dl and the dipole moments can be performed only in the series propazine, prometryne and prometone, and for atrazine and ametryne. It follows (Table IV) that dl is proportional to the dipole moments.
TABLE IV
COMPARISON OF -II VALUES AND DIPOLE MOMENTS No. Trivial name G3-, p
3 Propazine 489 4.52
13 Prometryne 459 3.54
8 Prometone 434 2.94
5 Atrazine 485 4.63
TABLE V RELATIVE ABUNDANCES (‘%) OF THE MAIN IONS ABOVE m/z 40 IN THE MONOISOTOPIC EI MASS SPECTRA OF MONOALKYLAMINO DERIVATIVES (d:, SCHEME 1) Superscripts .I. 1 and -3 indicate that lhcsc peaks wcrc fomd at 1 nmu. higher or 2 n,tn.u, lower, less than 0.5 ‘%,. rcspectivcly . ? = Not mnsurcd; - = not present or ..~ -. ..~ No. Trivitrl IUIIWZ M+’ [M - CH3J+ M+@ - h4+* - RzlJN cl/2 - G13 MS* - 6,/Z - HzN(HN)CkR, [Rz,JNH]+ [M - 2*CHJJac ((1) (Rz,J - H) d/(Jt (Rz - H) - R,’ [69 -I- R, J+ 2 3 4 5 G I 8 9 10 11 12 13 14 15 16 17 -. 13 33 29 I’~OpilZil~~ 39 74 25 Tcrbutylazinc 21 100 -151 Atrazinc 40 91 5/31 Norazine 12 29 2/15 Simzinc 65 4X 40 Promctonc 46 74 47 Tcrbufonc 18 100 2189 Atratonc 55 65 5/40 Noriltonc 28 40 9130 Sinictonc 100 47 42 Promctrync 66 55 29 Tcrbutrync 36 95 -/lOO An1e1rync 100 75 4134 Dcsmctrync 100 78 -/48 Sinictrync 100 22 17 ’ These ions arc coincident with 0, I- 1. N - (R2,, - H) (cd 100 - 50 2 4/l?. 2/- 18./14 412 l/3 l/2 23 5 75 20 4128 3/7 15’/24 4/15 IO/15 2122 55 74 87 18 6158 -I- 21 ‘136 9/18 -/18 -/18 41 41 f R, - I-r) ((1) . 5lf’ 10 12 II 1 12 34 28 15 9 27 16 17 II 8 (cd 7. 21 . 10 20 -/2O-2 I6 3/15 17 -/IO 3 19 11 - 23 - 10 - 10 - 8 - II 15 -/13+ I 1 8/14 - -125 - 20 - - 100 28/- 48/100 ?/lOO 100 100 17/2 60/100 ?/lOO 61 100 23/- 30176 ?/75 37 . 13 25 15 15 14 26 30 20 13 27 20 18 23 33 2 20 __-- - . .~ . .
Mass spectrometry
Electron-impact spectra. The positive ion electron-impact (EI) mass spectra
of the di(monoalkylamino)-s-triazine derivatives 2-17 are summarized in Table V. From these spectra a fragmentation scheme was deduced (Scheme 1).
PI - H]+ -
(R=
-
“L
(b=_I-l)[M-
R=]+OH-
/i”Ri
(al [t.l - .H3]+---'"~ M+- -[:
M_
q* . 41 -
'R=-
HI.
i -
'R=-
H)! -
(R= - HIp - CH3 - (RI - “9 +
-‘zH3
p -
(Rz-
Hg+-
-_Ri
+I - R1 - ‘Rx - tij *:C;_lJ (b I =-I (e x-1 I - RYN A - ‘Ry - HI k.1 - ‘R= - H) - R@- p - (Rx - H) - ‘Rr - Hfl +. (fj ( c 95 -I- R
11 )
(PlO + RJ+.l Cdl RzN --
‘Rg - HI c 69 + RScheme I. Fragmentation pathways for bis(monoaIkyIamino)triazine derivatives under EI conditions. s=Zor3;~=2if.r=3and~=3ifx=2.*: Transition is confirmed by metastable peaks. *: As c and c’ have the same nominal mass, it is unknown whether the metastable peak corresponds to the decomposition u -+ c or a + c’ or to both.
Only prominent peaks from the monoisotopic mass spectra are listed in Table V. Notable omissions include the followin,o. Ions M+- and b are accompanied by satellites at 1 a.m.u. lower with IO-20% of the abundance of the former ions. M’- loses R; [or (R, - H) in the case of methylthiotriazines], and c loses R,H to some extent (iess than 5% relative to these peaks). c loses CN- readily (up to 35% for chloro-, less than 10% for methoxy- and methylthiotriazines). In most spectra, the peaks corresponding in mass to d-15 and d-30 occur ([95 + RJ+- (f) and [SO + RJi- in Scheme I>.
stability, as function of Rx and Rx, decreases in the order Et,Et > E&i-Pr > i-Pr, i-Pr > Et,Bu (> Bu,Bu). The position of Mej-Pr compounds in this series is not clear because it is apparently influenced by the nature of R,. A comparison of the spectra of corresponding compounds with different R, groups shows that the stability of the compounds increases on electron impact in the order Cl < 0CH3 < SCH+:
The EI mass spectra of the diethylamino derivatives, triazines 19, 20 and 21, are given in Table VI. The deduced fragmentation pattern is depicted in Scheme 2.
(uJ
[M -
591' II
- c2H6 - (Et b I (ql[M -
HP---
l]'. -
H'\
i
M +. 29]+ Et' - (R2 - H) . - CR2 - HI (ul p - 28 - R2]+ i - Et' (*lI
-'CH3 -'CH3 (pl CM - 1q;J - CR2 - HI + (81) C M - 14 c R2 3 + . I - (Et - H) - (Et - H) CrJ [hl - 43]+ -(R -HI _' iuJ p /42 - RJ+Scheme 2. Fragmentation pathways for diethylaminotriazine derivatives and of sec.-bumeton under EI conditions. *: Transition is confirmed by metastabte peaks. Et equals R, (compounds 19,20 and
21) or part of R, (triazine 22).
Because sec.-bumetone (compound 22) fragments similarly on electron impact, this derivative is included in Table VI. However, its fragmentation also exhibits the path- ways proposed in Scheme 1.
Important peaks not included in Table VI involve the following ions. The loss of l+ from M+a results in an ion beam with about 10% of the intensity of M+-.
___. ~_ .-____ .-- __- -_-~-_.-. __-______---___ 4- 4- r- ~(CJWd!lc rRdffl+ [lu - 2’q]Z+ (M - ‘CK.. (Rz - ff) (4
:y6
(Rz - HI - -Er]- (w) _~___ _~..___ ~_.__ _._~~_.~ .___. 51 11 28 48 6719 11 9 8 9 6 36 23 8 11 6 88 24 4 - 3 *5+x=- 1 5 - 9/- 1 7 _- _~ __._~__._____ __-- A-. __-TADLE VI1 RELATIVE ABUNDANCES (%) OF TJ-lti MAJN IONS ABOVE nr/z 50 IN Tl-JE MONOlSOTOJ’IC CJ(Cl-Jd MASS SPECTRA OF MONOALKYL- AMJNO DERIVATIVES - = Not prcscnt or less than 0.5”/,, No. T&d mm [A4 -I- C,HJ+ MH+ M+@ MiI'+ - H, MN+ - CII., MI-I' -- R, II MI-I,+ - RJ" Mfl' - MH+ - HNRJ*' MH+ - R;H (4~ - H) - (R, - N)" 2 - 10 95 9 4 12 100 13 46 IO 3 3 Propzinc 13 70 9 3 I1 100 5 13 3 2 4 Tcrbutylnzinc 7 80 17 7 41 100 29 ‘8/E I I1 64 5 Atraeinc 19 98 II 6 I1 100 7 J/9 3 6 Nornzinc 15 100 7 2 3 94 2 -15 ! 1 7 Simnzinc 9 77 8 3 2 100 .- 3 1 1 8 Protlletonc 11 100 7 5 6 - 3 5 2 9 Tcrbutone 10 100 6 7 1 2 6 JO/30 1 10 Atratonc 13 100 6 5 4 - 2 -13 1 - 11 Noratone 12 100 5 5 4 I 2 -13 - - 12 Simctonc 1 I 100 8 7 3 1 3 2 - 13 Promctryne 15 100 9 5 6 1 2 5 2 1 14 Terbutrync 14 100 5 4 5 - 5 4124 1 15 Amctrync 15 100 7 6 4 2 2 -14 ! 1 16 Dcsmetrync 14 100 7 5 4 1 2 --I6 1 1 17 Simetrync 15 100 7 5 2 1 1 1 1 - _. _ _.._ _ ’ Corresponding losses of R2 were not foukl, . . . - - . - ._ --.
TABLE VIII RELATIVE ABUNDANCES (%) OF THE MAIN IONS ABOVE W/Z 50 IN THE MONOISOTOPIC CI(CH,) MASS SPECTRA OF DIETHYL- AMINO DERIVATIVES AND scc.*BUMETON - = Not present or less than OS%. No. Trividtrarrre [M-I- C2HJt MH+ M+' MH+ - H2 MN+ - CH, MN+ - R,H MH+ - C2Hb" MH+ - MH+ - R3' MH+ (Hz--ff) (R, .~. __ . ..___-_________.____--__-._ _.----...___..__--_-~-..~___ ..~~-.---. --..----._---. __.-_~....^..-..-- 19 lpnzinc 13 83 12 5 8 100 1 5 20 Trictazine 15 - 75 13 5 6 100 1 4 1* I., 21 Chlorazine 12 - 100 9 6 4 82 3 1 II **I) 22 set,-Bumetone 14 loo 4 7 6 8 5 ** 4 9 __- .--__-...--_-_..-.--___-- ._..._._- --._-...--_-- ..-.-... --. ._. -_-. ~. .- -.. -_.- -... ..___.. .- . . . -... .---_- .- .-___._ _._ ’ CIH6 equals RSH (compounds 19, 20,21) or pnrt of Rs (compound 22). ” Not corrected for isotopic contributions of MHf - CzH6. *” Coincident with MH+ - (R1 - H).
204 P. A. LECLERCQ, V. PACAKOVli Molecular ions M’* also lose R,*, yielding ions with an abundance of 5-10% of M +-_ In the spectra of diethylaminotriazines 19, 20 and 21, the following peaks in the low mass region were not included in Table VI: ~?z/z 99 [(CIH&HCN], l&49%; mjz 71 ([CzHSN=CH,]‘-), 15-36%; m/z 69, 29-50%; mjz 68, 43-68%; m/z 55, 32-53 s: I&Z 43, 5 l-75 % ; mJz 42, 28-43 5; and nz/z 41, 7-28 %. The elemental composition of t-he latter ions is presumably the same as that described earlier for di(monoalkylamino) compounds. All of these ions bvere far less abundant in the spec- trum of sec.-bumetone (less than 4 %, except nz/z 68, 8 % and nr/z 43, 11%).
The spectrum of sec.-bumetone does not show a peak corrresponding to ion II from Scheme 2 [Mi. - -C,H, - (R2 - H-)] but rather to M+= - (R, - H) at 1 a-m-u. higher (6,, Scheme 1).
TABLE IX
RELATIVE ABUNDANCES (92) OF THE MAIN IONS ABOVE nz/= 70 IN THE MONOISOTOPIC CI (ISOBUTANE) MASS SPECTRA OF MONOALKYLAMINO DERIVATIVES
-= Not present or less than 0.5%.
;V0. Trivial name i&Z -L C,HJ+ !-IV - C,H,j+ [Al ; C,Hsj+ [LCf + C,H,j’
2 3 4 5 6 7 s 9 10 11 12 13 14 15 16 17 - - Propazine - Terbutylazine - Atrazine Norazine - Simazine - Prometone 1 Terbutone 1 Atratone 1 Noratone 1 Simetone 1 Prometwne 1 TerbEtqne 1 Ametryne 1 Desmetryne ! Simetryne 1 i 1 1 1 1 1 2 1 1 2 2 2 2 2 2 2 1 I I 1 1 1 1 1 1 1 1 1 1 1 1 1 3- 3 3 2 3 2 3 3 2 2 3 3 3 3 3 3 100 100 100 100 100 100 100 100 100 loo 100 loo 100 100 100 100 9 7 7 7 7 7 7 7 7 6 7 8 S 7 7 6 * Corresponding losses of Rz were not found.
TABLE X
RELATIVE ABUNDANCES (3;) OF THE MAIN IONS ABOVE w/z 70 IN THE MONOISOTOPIC CI (ISOByT.4NE) MASS SPECTRA OF DIETHYLAMINO DERIVATIVES AND sec.-BUMETON
- = Not present or less than 0.5%.
19 lpazine - 2 2 3 100 .8 20 Trietazine 1 2 2 3 l@O 8 21 Chlorazine - 2 1 1 loo 5 22 sec.-Bumetone 1 1 1 3 100 7 ’ Coincident with MH’ - C,H,. l - MH* - C,H,. -*- MH+ - C,Hg.
Ions q, r, u and IV are presumably identical with the corresponding ions
M+* - H., n, b - H and c from Scheme 1. Metastable peaks were observed for
several transitions, as indicated in Scheme 2. The main fragmentation process is the
Ioss of C,H, from M’-, yielding the base peak in all instances_
A comparison of the spectra of triazines 21, 20 (Table VI) and 7 (Table V)
shows that the abundance of the molecular ions decreases with increasing number of
ethyl substituents. In other words, simazine is more stable on electron impact than
trietazine, which in turn is more stable than chlorazine. This substituent effect is
reversed, however, with ipazine, which seems to be more stable than atrazine. A
reason for this phenomenon has not been found.
~- - ,LfH+ - H2 XfH+ - CH, MH l - %fH- - R,H AfH’ - XIH- - MH + -CR,- H) (R, -H) CR3 - H)’ R,-.’ -CR, - H)! - R,H’ --- -.--- - .________ --__ - 1 3 1 5 1 l/l - 1 z 1 1 - l/l - 1 2 1 4 l/l - 1 1 1 - -/- - 1 1 1 - - _/- - - 1 1 - - -/I - 1 - 1 1 -/- 1 1 - - 22 1 -/- - 1 - - 1 -I- - 1 - - - 1 -I_- 1 - - - - 1 -/- 1 1 1 - - - -/- l 1 1 - 3 1 -!- 1 1 1 - - _i- 1 - 1 - - _;- - 1 - - - _I_ -_.- -~----__
:\fH+ - CH, i1.f H + - (Ii, - H)- hiH+ -- R,H AfH- -- C2H4 .\lH- - kIHo i!lH’ - /R, - H) - C,H+’ - C,H, 2 -I - 1 ; 1 1 !I 1 1 1 - 2 -I 1 1 2’ 1 . A---_ - _ __ _._______ 1 ._~ _ _. ~_ 1 1 . . . ;l . . .
206 P. A. LECLERCQ, V. PACAKOVA
Chemical-ionization spectra. The chemical-ionization (CI) mass spectra, using methane as reagent gas, are summarized in Tables VII and VIII. In these tables adduct ions [M + C,H,]+ have been omitted; their abundance was less than 4% in all instances . Ions MH’ - C,H4, observed in the spectra of triazines 2 (13 %), 6 (3 %) and 11 (1473, also have not been included. Finally, triazine 2 displayed a peak corresponding to MH’ -.(R? - H) - (R3 - H):l6%.
For the protonation in the gas phase, the negative enthalpy of the reaction (- dH”) is defined as the proton affinity (PA) of the molecule. The enthalpy for the reaction CH$ + M -+ MH’ + CH4 then equals the difference in the proton affini- ties of the sample and the reagent gas molecules: .4H” = PA(CH*) - PA(M). The degree of fragmentation of protonated molecular ions MH+ can generally be cor- related with the amount of the ener_gy exchanged in the protonation reaction (AH’) and hence with the proton affinities of the sample and the reagent gas molecules. Table VII shows that 2-chloro-s-triazines fragment much more easily than the methoxy and thiomethyl derivatives. The conclusion that the PA of the triazines decreases in the order Cl > OCH, > SCH, is, however, false. The proton affinities are proportional to the gas-phase basicitiesZ6*“. Although they are infiuenced by solvent effects, the solution phase basicities (pK, values) show a different order: OCHj > SCH, > Cl. The PA data available for RCl, ROCH3 and RSCH3 com- pounds are analogous to the order of the solution-phase basicities” (see also Table XI). Another possible conclusion, that fragmentation of a given MH’ decreases whenever reactant gases with higher PA are applied, is correct, as can be seen, e.g., for the methane (Tables VII and VIII) and isobutane (Tables IX and X) CI mass
spectra [PA(CH,) = 129 kcal/mol; PA(i-C,H,,) = 195 kcal/mol].
Other factors govern the fragmentation mechanism. FieldZg has already sug- gested that the leaving ability of a group R from a given compound M is inversely proportional to the proton afinity of RH. This has been confirmed for a series of cyclohexyl derivatives30 and for series of substituted 1,4-oxathiins and derivatives31_ The follo\ving rationale is proposed for the fragmentation of the triazines under CI (methane) conditions, by analogy with the cited reports. Protonation takes place preferentially on the alkylamino groups (the PA of HzNR is very high: Table XI), or possibly on the triazine-ring nitrogen atoms. Hydrogen rearrangements may occur in protonated molecular ions before decomposition occurs30. The loss of a neutral molecule R,H from MH’ may then occur. The importance of this fragmenta- tion (Table VII) is indeed inversely correlated Lvith the proton affinity of the departing R,H molecule (Table Xl).
TABLE XI
PROTON AFFINITIES (P/l) OF SOME SELECTED MOLECULES
R = alkyl.
H,NR 2 1 Y-226 25
CH,SH IS5 77
CHAOH 180 27
The electron-releasing inductive effect of alkyl groups is proportional to the proton affinity of the nitrogen atom attached to themZ6. This explains the abundance of the ions MH+ - (R3 - H) in the case of tert.-butylamino derivatives.
CI mass spectra, obtained with isobutane as reagent gas, are. listed in Tables IX and X. Ions MH+ are the base peaks in all of the spectra. Adduct ions and fragment ions contribute relatively little to the total ion current. Apart from M+=, the only fragment ions of importance correspond to the loss of isobutene from MH+ in the spectra of terr.-butyl derivatives. Remarkable, but not yet understood, is the loss of (R, - H) from MH+, especially with chlorotriazines.
ACKNOWLEDGEMENTS
We are obliged to Dr. E. Matisova of the Slovak Technical University for kindly supplying us with many of the s-triazines. The contribution of Mr. J. Bakker, Eindhoven University of Technology, in obtainin, m the chemical-ionization mass spectra is acknowledged_ This work was supported by the Scientific Exchange Agreement (SEA).
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