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Identification of the order of aromatic alcohols and their derivatives by means of thin-layer chromatography
MICROCHEMICAL
.JOURK.AL
23, 384- 389 (1978)
Identification of the Order of Aromatic Alcohols and Their Derivatives by Means of Thin-Layer Chromatography J~ZEF~LIWIOKAND Institute
of Chemistry,
Silcsian Received
LEONARD~GIERMAN University,
40-006 Katnwicc,
Poland
April 25, 1978
In a number of papers dealing with thin-layer chromatography a linear correlation has been established between the R, coefficient values and the number of methylene groups in a molecule of investigated compounds (I -6). This fact enabled identification of individual components of the selected homologous groups (I, 3, 5). Our paper takes advantage of the a/m dependence and concerns determination of the order of aromatic alcohols as well as of their esters on a thin layer. EXPERIMENTAL
Separation of the selected aromatic alcohols and their acetates by means of adsorption thin-layer chromatography was performed using the ready-made glass plates (E. Merck, West Germany), covered with a 0.25 mm-thick 60-Fzs4silica gel and activated for 30 min at 110°C. The following mobile phases were applied: alcohols: (A) cyclohexane-dichloroethane-ethyl acetate (v/v/v, 4: 1:1); (B) Carbon tetrachloride-ethyl ether-ethyl acetate (v/v/v, 82: l), esters: (C) cyclohexane-benzene-chloroform (v/v/v, 8: 1:1); (D) n-hexane-carbon tetrachloride-ethyl ether (v/v/v, 8: 1: 1). Chromatograms were visualized under uv light, wave length of 254 nm, or with a 5% solution of phosphoromolybdic acid. RESULTS
The results of separation of aromatic alcohols as well as of their acetates are given in form of the Rf and R, coefficients in Tables 1 and 2. DISCUSSION
The R, values of the examined homologous groups of aromatic alcohols and their acetates show a linear correlation based on the number of car384 0026-26.5X/78/0233-0384$01.00/0 Copyright All rights
@ 197X by Academic Presc. Inc. of reproduction in any form reserved.
AROMATIC
ALCOHOLS
AND
TABLE THE
R, AND R,
COEFFICIENT
VALUES
Separated substances Primary alcohols Benzyl alcohol 2-Phenylethanol 3-Phenyl- I-propanol 4-Phenyl-1-butanol Secondary alcohols I-Phenyl-l-ethanol I-Phenyl- I-propanol I-Phenyl-l-butanol I-Phenyl-1-pentanol Tertiary alcohols 2-Phenyl-2-propanol
1
OF THE AROMATIC
THIN-LAYER
385
DERIVATIVES
ALCOHOLS
IN THE ADSORFWOX
CHROMATOGRAPHY
Mobile phase (A)
Mobile phase (B)
Rf
RI
RlZ (X102)
RVt (X 102)
35.4 30.3 26.4 22.0
26.1 36.2 44.5 55.0
44.1 38.7 34.1 29.9
10.5 20.0 28.6 37.0
44.3 52.4 59.2 65.8
10.0 - 4.3 -16.2 -28.4
53.9 60.5 68.0 73.7
- 6.8 -18.5 -32.7 -44.7
12.6
-42.3
79.1
-57.8
bon atoms in a molecule. This dependence is given in Figs. 1 and 2 and remains unchanged for all the applied mobile phases. Simultaneously it seems significant that the discussed dependence R,
THE
R, AND R,
TABLE 2 Acr’rArEs
COEFFICIENT VALUES OF THE ADSORPTION THIN-LAYER
OF AROMATIC CHROMATOGRAPHY
Mobile phase (C) R,
Rf Separated substances Acetates of primary alcohols Benzyl alcohol 2-Phenylethanol 3-Phenyl- I-propanol 4-Phenyl-I-butanol Acetates of secondary alcohols I-Phenyl- I-ethanol I-Phenyl- I-propanol I-Phenyl-l-butanol I-Phenyl-1-pentanol Acetates of tertiary alcohols 2-Phenyl-2-propanol
ALCOHOLS
IN THE
Mobile phase (D) 4
R, (X102)
(X 102)
36.2 31.6 28.0 23.4
24.6 33.5 41.0 51.5
49.6 44.2 38.7 32.8
0.7 10.1 20.0 31.2
43.1 48.8 53.6 57.8
12.0 2.0 - 6.3 -13.6
60.6 66.5 71.2 75.4
- 18.7 -29.8 -39.3 -48.7
65.9
-28.6
82.7
-67.9
386
SLIM’IOK
7 ,
FIG.
Alcohols
0
Esters
of carbon Q
a’
atoms lo
Esters
9’
1, The R,,! coeffkient
OCIERMAN
Number
Alcohols
201
their
0
AND
io
values
vs the number
12
II
of carbon
atoms
for primary
alcohols
and
acetates.
=f(c) for two mobile phases (A) and (B) in the case of alcohols and (C) and (D) in the case of esters demonstrates the parallel course. Presentation of the results in form of the R, coefficient dependences for both mobile phases also shows a linear correlation, no matter what the order of the examined homologous orders of alcohols and their acetates are. The above-mentioned dependence is given in Figs. 3 and 4. With the separation of primary alcohols and their esters, changes in adsorption of the individual homologs are caused by increases of the carbon side chain length, and they induce lowering of the R, values. For the homologous order of secondary alcohols and their esters, one observes the reverse effect. In this case separation of a single species is influenced by steric effects to a greater extent. Thus the hydroxyl and ester functional groups are less adsorbed on a layer, which is reflected in the increased Rf values. In the discussed homologous order the Rf coefflcient value increases with the growing length of the carbon side chain. The highest & coefficient values are characteristic of the tertiary alcohols and their esters, where the functional group is sterically hindered to the highest extent.
AROMATIC
0
20
ALCOHOLS
AND
387
DERIVATIVES
Alcohols
i
Number
Alcohols
-60 6 I
Esters
to
FIG. 2. The R,,, coeffkient and their acetates.
of carbon
atoms
9
to
Ii
11
12
t3
values vs. the number of carbon atoms for secondary alcohols
The results of chromatographic separation of the investigated homologous orders shown in the form of the mutual dependences of R,, coefficents demonstrate a linear course with all groups of alcohols and the corresponding esters. The a/m fact presented in Figs. 3 and 4 is evidence of the regularity with which substances belonging to the same group of chemical compounds, but differing with respect to functional group order, can be characterized by the constant value of the R,, change in the same two mobile phases. A constant parameter will also be given by the ratio of the R, value differences for two homologs, determined in two mobile phases. The discussed dependence is given by the following equation: R ma tB)- R ml3 (B) (;\,= tga = const. R maC.4)_ R nlP In this equation use was made of determinations presented in Fig. 3, in which: RmacA',R,B(A), R,,'B', and R,LI(B' are the R, values for the (Yand p substances determined in the (A) and (B) mobile phases.
388
SLIWIOK
4c
AND
pr,mary
0
secondary
l
tert1Clry
e
OGIERMAN
2c
0
-20
-40
-60
R,*
- 40 FIG.
-20
lo’
0
for
the
20
moblle
phase
(A)
40
3. The R, coefficient values for aromatic alcohols in two mobile phases.
On the basis of the conducted investigations the possibility of determining functional group order of aromatic alcohols and their esters was established, employing the chromatographic results. Using data arranged in form of the R, = f(c) function, obtained for two different mobile phases, as well as data obtained on the basis of the linear correlation between the R, coefficients in the (A) and (C) mobile phases vs the similar coefficients in the (B) and (D) mobile phases, a new method has been established of distinguishing the functional group order of the discussed homologs. SUMMARY Separation conditions for homologous orders of primary and secondary aromatic alcohols as well as their acetates were established applying adsorption thin-layer chromatography. A linear correlation was found for the R, coefficient values depending upon the number of carbon atoms in the analyzed homolog. In addition it was established that the R, coefficient values of aromatic alcohols in two mobile phases demonstrate a linear dependence, regardless of the order of the examined homologous groups.
AROMATIC
primary
ALCOHOLS
AND
389
DERIVATIVES
0
secondary
0
tert,ary
0
-60
/ e
-60
FIG.
1
Cl1
R,*
-26
4. The R, coefficient
0
lo2
2;
for
the
mobile
4;
phase(C)
6;
-
values for acetates of aromatic alcohols in two mobile
phases,
REFERENCES 1. Bark, L. S., The R, function and its use in structural analysis of organic compounds. Progr. Thin-Layer Chromatogr. Relaf. Methods 1, l-5 1 (1970). 2. Graham, R. J. T., and Daly, J., The behaviour of ethyl, propyl and butyl homologues of phenol on layer of cellulose impregnated with simple amides. J. Chromarogr. 48, 78-89 (1970). 3. OScik, J., Correlation of the R, values in partition and adsorption chromatography. Bull. Acad. Pol. Sci. Ser. Sci. Chim. 14, 879-883 (1966). 4. Prochazka, Z., The determination of the structure of organic compounds by chromatography. R, function as a basis for structural analysis using chromatography. Chem. Listy 58, 911-945 (1964). 5. Simon, J., and Lederer, M., Identification of substances by thin-layer chromatography in one solvent on a range of layers. J. Chromatogr. 63, 448-451 (1971). 6. Soczewinski, E., and Bieganowska, M., Two homologous series of pyridine derivatives suitable as reference compounds in liquid-liquid partition chromatography. J. Chromatogr. 40, 431-439 (1969).
.JOURK.AL
23, 384- 389 (1978)
Identification of the Order of Aromatic Alcohols and Their Derivatives by Means of Thin-Layer Chromatography J~ZEF~LIWIOKAND Institute
of Chemistry,
Silcsian Received
LEONARD~GIERMAN University,
40-006 Katnwicc,
Poland
April 25, 1978
In a number of papers dealing with thin-layer chromatography a linear correlation has been established between the R, coefficient values and the number of methylene groups in a molecule of investigated compounds (I -6). This fact enabled identification of individual components of the selected homologous groups (I, 3, 5). Our paper takes advantage of the a/m dependence and concerns determination of the order of aromatic alcohols as well as of their esters on a thin layer. EXPERIMENTAL
Separation of the selected aromatic alcohols and their acetates by means of adsorption thin-layer chromatography was performed using the ready-made glass plates (E. Merck, West Germany), covered with a 0.25 mm-thick 60-Fzs4silica gel and activated for 30 min at 110°C. The following mobile phases were applied: alcohols: (A) cyclohexane-dichloroethane-ethyl acetate (v/v/v, 4: 1:1); (B) Carbon tetrachloride-ethyl ether-ethyl acetate (v/v/v, 82: l), esters: (C) cyclohexane-benzene-chloroform (v/v/v, 8: 1:1); (D) n-hexane-carbon tetrachloride-ethyl ether (v/v/v, 8: 1: 1). Chromatograms were visualized under uv light, wave length of 254 nm, or with a 5% solution of phosphoromolybdic acid. RESULTS
The results of separation of aromatic alcohols as well as of their acetates are given in form of the Rf and R, coefficients in Tables 1 and 2. DISCUSSION
The R, values of the examined homologous groups of aromatic alcohols and their acetates show a linear correlation based on the number of car384 0026-26.5X/78/0233-0384$01.00/0 Copyright All rights
@ 197X by Academic Presc. Inc. of reproduction in any form reserved.
AROMATIC
ALCOHOLS
AND
TABLE THE
R, AND R,
COEFFICIENT
VALUES
Separated substances Primary alcohols Benzyl alcohol 2-Phenylethanol 3-Phenyl- I-propanol 4-Phenyl-1-butanol Secondary alcohols I-Phenyl-l-ethanol I-Phenyl- I-propanol I-Phenyl-l-butanol I-Phenyl-1-pentanol Tertiary alcohols 2-Phenyl-2-propanol
1
OF THE AROMATIC
THIN-LAYER
385
DERIVATIVES
ALCOHOLS
IN THE ADSORFWOX
CHROMATOGRAPHY
Mobile phase (A)
Mobile phase (B)
Rf
RI
RlZ (X102)
RVt (X 102)
35.4 30.3 26.4 22.0
26.1 36.2 44.5 55.0
44.1 38.7 34.1 29.9
10.5 20.0 28.6 37.0
44.3 52.4 59.2 65.8
10.0 - 4.3 -16.2 -28.4
53.9 60.5 68.0 73.7
- 6.8 -18.5 -32.7 -44.7
12.6
-42.3
79.1
-57.8
bon atoms in a molecule. This dependence is given in Figs. 1 and 2 and remains unchanged for all the applied mobile phases. Simultaneously it seems significant that the discussed dependence R,
THE
R, AND R,
TABLE 2 Acr’rArEs
COEFFICIENT VALUES OF THE ADSORPTION THIN-LAYER
OF AROMATIC CHROMATOGRAPHY
Mobile phase (C) R,
Rf Separated substances Acetates of primary alcohols Benzyl alcohol 2-Phenylethanol 3-Phenyl- I-propanol 4-Phenyl-I-butanol Acetates of secondary alcohols I-Phenyl- I-ethanol I-Phenyl- I-propanol I-Phenyl-l-butanol I-Phenyl-1-pentanol Acetates of tertiary alcohols 2-Phenyl-2-propanol
ALCOHOLS
IN THE
Mobile phase (D) 4
R, (X102)
(X 102)
36.2 31.6 28.0 23.4
24.6 33.5 41.0 51.5
49.6 44.2 38.7 32.8
0.7 10.1 20.0 31.2
43.1 48.8 53.6 57.8
12.0 2.0 - 6.3 -13.6
60.6 66.5 71.2 75.4
- 18.7 -29.8 -39.3 -48.7
65.9
-28.6
82.7
-67.9
386
SLIM’IOK
7 ,
FIG.
Alcohols
0
Esters
of carbon Q
a’
atoms lo
Esters
9’
1, The R,,! coeffkient
OCIERMAN
Number
Alcohols
201
their
0
AND
io
values
vs the number
12
II
of carbon
atoms
for primary
alcohols
and
acetates.
=f(c) for two mobile phases (A) and (B) in the case of alcohols and (C) and (D) in the case of esters demonstrates the parallel course. Presentation of the results in form of the R, coefficient dependences for both mobile phases also shows a linear correlation, no matter what the order of the examined homologous orders of alcohols and their acetates are. The above-mentioned dependence is given in Figs. 3 and 4. With the separation of primary alcohols and their esters, changes in adsorption of the individual homologs are caused by increases of the carbon side chain length, and they induce lowering of the R, values. For the homologous order of secondary alcohols and their esters, one observes the reverse effect. In this case separation of a single species is influenced by steric effects to a greater extent. Thus the hydroxyl and ester functional groups are less adsorbed on a layer, which is reflected in the increased Rf values. In the discussed homologous order the Rf coefflcient value increases with the growing length of the carbon side chain. The highest & coefficient values are characteristic of the tertiary alcohols and their esters, where the functional group is sterically hindered to the highest extent.
AROMATIC
0
20
ALCOHOLS
AND
387
DERIVATIVES
Alcohols
i
Number
Alcohols
-60 6 I
Esters
to
FIG. 2. The R,,, coeffkient and their acetates.
of carbon
atoms
9
to
Ii
11
12
t3
values vs. the number of carbon atoms for secondary alcohols
The results of chromatographic separation of the investigated homologous orders shown in the form of the mutual dependences of R,, coefficents demonstrate a linear course with all groups of alcohols and the corresponding esters. The a/m fact presented in Figs. 3 and 4 is evidence of the regularity with which substances belonging to the same group of chemical compounds, but differing with respect to functional group order, can be characterized by the constant value of the R,, change in the same two mobile phases. A constant parameter will also be given by the ratio of the R, value differences for two homologs, determined in two mobile phases. The discussed dependence is given by the following equation: R ma tB)- R ml3 (B) (;\,= tga = const. R maC.4)_ R nlP In this equation use was made of determinations presented in Fig. 3, in which: RmacA',R,B(A), R,,'B', and R,LI(B' are the R, values for the (Yand p substances determined in the (A) and (B) mobile phases.
388
SLIWIOK
4c
AND
pr,mary
0
secondary
l
tert1Clry
e
OGIERMAN
2c
0
-20
-40
-60
R,*
- 40 FIG.
-20
lo’
0
for
the
20
moblle
phase
(A)
40
3. The R, coefficient values for aromatic alcohols in two mobile phases.
On the basis of the conducted investigations the possibility of determining functional group order of aromatic alcohols and their esters was established, employing the chromatographic results. Using data arranged in form of the R, = f(c) function, obtained for two different mobile phases, as well as data obtained on the basis of the linear correlation between the R, coefficients in the (A) and (C) mobile phases vs the similar coefficients in the (B) and (D) mobile phases, a new method has been established of distinguishing the functional group order of the discussed homologs. SUMMARY Separation conditions for homologous orders of primary and secondary aromatic alcohols as well as their acetates were established applying adsorption thin-layer chromatography. A linear correlation was found for the R, coefficient values depending upon the number of carbon atoms in the analyzed homolog. In addition it was established that the R, coefficient values of aromatic alcohols in two mobile phases demonstrate a linear dependence, regardless of the order of the examined homologous groups.
AROMATIC
primary
ALCOHOLS
AND
389
DERIVATIVES
0
secondary
0
tert,ary
0
-60
/ e
-60
FIG.
1
Cl1
R,*
-26
4. The R, coefficient
0
lo2
2;
for
the
mobile
4;
phase(C)
6;
-
values for acetates of aromatic alcohols in two mobile
phases,
REFERENCES 1. Bark, L. S., The R, function and its use in structural analysis of organic compounds. Progr. Thin-Layer Chromatogr. Relaf. Methods 1, l-5 1 (1970). 2. Graham, R. J. T., and Daly, J., The behaviour of ethyl, propyl and butyl homologues of phenol on layer of cellulose impregnated with simple amides. J. Chromarogr. 48, 78-89 (1970). 3. OScik, J., Correlation of the R, values in partition and adsorption chromatography. Bull. Acad. Pol. Sci. Ser. Sci. Chim. 14, 879-883 (1966). 4. Prochazka, Z., The determination of the structure of organic compounds by chromatography. R, function as a basis for structural analysis using chromatography. Chem. Listy 58, 911-945 (1964). 5. Simon, J., and Lederer, M., Identification of substances by thin-layer chromatography in one solvent on a range of layers. J. Chromatogr. 63, 448-451 (1971). 6. Soczewinski, E., and Bieganowska, M., Two homologous series of pyridine derivatives suitable as reference compounds in liquid-liquid partition chromatography. J. Chromatogr. 40, 431-439 (1969).