556
JOURNAL
CWROM,
OF CWROMATOGRAPHV
5793
Calculation of retention indices for benzene and benzene derivatives
basis of maleeular structure
on the
The Kovats retention index system for the presentation of gas chromatographic
data has become widely used l. Methods have been proposed for the prediction of
retention indices based on boiling point or other physical data2J. Other studies have
been made to determine the relationship between molecular structure and retention
inde&s. Once this relationship has been determined the prediction of retention
indices, is quite accurate. Most of the previous studies were concerned with aliphatic
hydrocarbons. For this reason, an investigation of benzene, its derivatives and, the
retention indices of these compounds was undertaken.
Ex$erimentat?
A Beckman GC-2 gas chromatograph equipped with a thermal conductivity
detector was used to determine the retention indices. The carrier gas was helium and
was used at a flow-rate of cu. 40 ml/min; the exact flow-rate was measured with a
soap-bubble flow meter. Retention times were recorded using a Leeds and Northrup
Speedomax X/L 680 recorder. The columns were operated isothermally at temperatures of JCOO’,130~ and 160~. Because of the lack of column stability at high temperatures, the squalane column was operated only at IOOOand 130~.
Squalane (Supelco Inc.), SE-30 (Applied Science Laboratories) and Apiezon L
(Applied Science Laboratories) were used as stationary phases. A 20% loading on
Chrom.osorb IV (acid-washed, DMCS-treated, 80-100 mesh) was used for all columns.
The columns ,were 6 ft. in length and made of I/4-in. 0.D. copper tubing.
The liquid samples were obtained from various commercial sources, were of the
highest purity available and were introduced into the column by means of a Hamilton
71orN syringe. ‘The sample size was 0.5 ,~l. The amine compounds were distilled and
purified before use.
Results
and dkcussion
qor monosubstituted benzene derivatives, the Kovats retention index can be
considered to consist of two additive parts: the aromatic ring contribution (I&,) and
the substituent contribution (Is). Therefore,
Ig.Dh. (T) & JB,t.Ph*
(2”) + l;Wl. (T)
(I)
where Is = retention index of the monosubstituted benzene derivative at a particular
temperature and stationary phase (st. ph.) and T is the column temperature, The
retention index for benzene and monosubstituted benzene derivatives on a particular
stationary phase at a given temperature can be found in the usual mannerl. Then, by
rearranging eqn. r, the I;t*~rl*contributions can be determined:
J. Ch+omalogv.,G$ (1972) 556-55g
.I
;
.”
NOTES
557
‘For example, on an SE-30 column at 130°, benzene has an index value of 669 i.u.
and bromobenzene
has an index value of 943 i.u. Utilizing eqn. 2, the bromo group
is assigned an index value of 274 i.u.
This procedure was used to calculate the I;t*@. values for twenty-seven
benzene
RETENTION
INDIClr,S
COI-I, (unsubstitUtXXl)
--CH,
-cl-I,cI-J,
-CI-I,CI-I&H-I,
-cI-1&3-1,)&1-r,
-CH&I-I
(CH,) 3
-C(CH,I,
-CI-I(CM,),
-I
-Br
-Cl
--I?
-0CEI,
-CN
-NT-I,
-Cl-IO
.
-z
cl-ra
-CH;OCI-I:,
-CI-I,OW
-CM,CI
-COCN,
-NO,
-CH~COOCT~r,,
-CT-I,CEI,Br
-coocI-I&I-I,
-CI-I&I-I,OI-I
-CT-I,Rr
-CH&N
FOR
DEN%IINE
AN13
IN13IVIl3Uh’I,
690
680
II2
110
203
292
209
290
110
200
288
391
343
329
388
339
323
259
419
296
196
700
261
432
304
204
-14
243
28s
289
28s
321
303
327
y 2
41O
43G
541
469
409
445
420
-10
24.0
281
282
279
31G
304
323
345
379
338
322
256
28s
I92
4
24=
274,
277
274
32”
301
319
402
437
532
470
402
435
4.15
-
SUI%STITUSSNT
675
104
203
290
394
350
337
669
26G
390
282
194
5
247
313
303
294
317
316
357
349
395
421
476
529
441
433
455
GROUPS
a.52
103
199
291
390
346
331
6‘19
656
104.
200
108
108
200
29t
290
199
258
388
343
328
390
344
328
3%
342
326
262
261
260
240
378
274
186 e
3G?
267
385
273
375
2G7
229
-4
229
250
248
2.50
246
249
311
186
245 ’
303
297
284
313
24 4
307
3oo
287
313
31G
354
342
389
411
475
517
489
433
422
446
181
181
4
8
6
253
312
313
353
338
354
403
WG
294
295
323
353
3GG
429
503
457
379
407
381
293
31s
351
3Go
=
-.
substituents
on three different columns at loo”, 130’ and 160~. The results are given
in Table 1.
between 100’
To determine the I;t*phe values for groups at any temperature
and
160°,
plots
of I;t~Db* VS. temperature
can be made.
Fig.
I
shows
a
number
of
18t.P”. 7)s. temperature
plots on an SE-3b column.
8
An interesting point is the fact that benzene (b.p. 130.1”) is retained longer on
(b.p. 85”). However, fluorothe squalane and Apidzon L phases than is fluorobenzene
benzene is eluted before benzene on the SE-30 column.
An investigation
was undertaken
to determine
the correlation
between the
J. Ckvomalo~v., 65 (1972)
556-559
NOTES
-CN
.
.
e.
-NH2
I
130
Temperature
I
160
-
(“C)
retention
index for cli- and tri-substituted
benzene derivatives
and the calculated.
l~~~)h~ values. It was proposed that the retention
indices for these compounds
could
b8e predicted
Therefore :
by adding
=
qg!&JT)
the contributions
pprm.
(T)
+
of the individual
~qt.Pll.
substituent
values.
(3)
To test this equation, a number of di- and tri-substituted
benzene derivatives
were injected and their measured retention index values compared with the predicted
values.
The predicted
retention index for o-l~romoanisole
on an SE-30 column at lGoo
TAl3LYz II
COMPARISON
012 OHSERVED
AND
I’RILDICTED
Compoacnd
Ia
j%Brotnoanisole~
~-Mcthyla.cctophenorlcC
z-Bromo-I,3,5-trimct;hylbcnzencd
z-Clrloro-p-xylcnco
2-Bromo-p-xylcncf
I-Cllloro-2-ioclobcnzcnef
o-ToluiclincR
3,5-Dimcthylanisolc~
12zG
--
L Prcclictcd.
b Obscrvcd.
(J hpiozon L at 230’.
d Squdano at: 130~.
0 Squalnnc at 100~.
r SE-30 at IGOO.
8 SE-30 at 130~.
J.
Chvomaiogv,,
RIZTIENTION
65 (1972) 556-559
1179
I253
1044
1212
1259
1014
1119
I”
1224
1187
1254
1046
12x0
2257
1013
11X1
INDICISS
NOTES
559
is founcl by aclding the contributions
benzene. From Table I :
of the horn0
and methoxy
groups
to that
of
i.u.
It$-30
(160”)
=
282
.ppafJ
(I&“)
=
675 i.u.
Total
=
1204 i.L
The experimental
value found was 1202 i.u. A number bf other predicted
and experimental values are summarized
in Table II. An at!empt
was made to determine
the
effect of the ring position of the substituent
groups on the retention index; a number
of isomers were studiecl but no comm.on factor coulcl be founcl.
This research
was supported
by the
graduate
Research
Participation
Program.
De;l,art?nent of Chewaistry,
Grand Forlw, ND. 58201
National
Science
T.AWRI?NCE
(U.S.A
Minla. 5por
FRANK
(US.A.)
E.
KovhTs,
Hslv. CMrl. Acta, 41 (1958) ~grg.
N. IIIMOV
AND
D.
~~IoI’ov,
,J, Chvonzato~r., 44 (IgO@
170.
3 1'.R0r3INs0N
AND
A.
L.
ODELL,
J. Cl~ronzato~r., 57 (1971) I.
4 G. CAs’rELLo AND G. D’AMATO,
J. Clcrozwatop.,
58 (1971) 127.
5 J. *rhl<r(cs,
c.
SZITA,
AND
C;. TARJhN,
.J. CJJYOW~~O~V.,
gG (rg7j)
I
2
Rcceivecl
October
18tll,
1971
Uncler-
@.
COOK
.)
College of St. Thomns,
St. Pad,
Foundation
J.
M. RAUSWEL