STRUCTURE AND PERFORMANCE PROPERTY RELATIONS OF STRAIGHT-CHAIN ALKYLBENZENES Pure Isomer Correlations JOSEPH
RUBINFELD, E. M . EMERY,‘ AND H . D . CROSS I l l
Research and Development Department, Colgate-Palmoliae Co., Jersey City,
J.
A relationship between commercial mixtures of straight-chain alkylbenzenes and their ultimate performance as sulfonates in detergent products has been established through studies of many pure and nearly pure fractions of isomers. In heavy-duty systems, the optimum performance for 2-phenyl sulfonates occurred at chain lengths of c13 and C14 a t 50-and 150-p.p.m. water hardnesses. Sulfonates of the 5-,6-, and 7phenyl (internal) isomers also peaked at these same chain lengths in 50-p.p.m., but shifted the optimum to Ci? and C13 chains in 150-p.p.m. hardness. Within the range of optimum chain lengths (Clz to C15) the internal isomers were substantially superior in performance at both hardnesses. For a light-duty formulation, all phenyl isomers showed best performance in the C i i to CIS chain lengths. The 2-phenyl isomers were most sensitive to hardness in this case, with the internal isomers remaining the superior performers. NVESTIGATIOSS
of factors affecting performance characteris-
I tics of surfactants have been under way in these laboratories
for many years. .4s little as a year ago, alkylbenzene sulfonates prepared by sulfonating the alkylation product of benzene with propylene tetramer (commonly termed ABS) represented a very important constituent of household detergents. ABS, with its relatively highly branched alkyl chains and its performance pluses, lacked the very important and currently requisite property-biodegradability. T h e addition of biodegradability as a vital performance criterion thus stimulated the transition from ABS to straight-chain alkylbenzene sulfonates (known as linear alkylate sulfonate, LAS) or to other biodegradable materials. A recent publication from these laboratories stated that mass spectral analyses of commercial mixtures of branched alkylbenzenes were successfully correlated Ivith their ultimate effect as sulfonates in finished products ( 3 ) . T h e principal theme of that same w0r.k was the equally successful correlation of the mass spectral analysis of commercial straight-chain alkylbenzenes to the performance of their sulfonates. Directly comparable investigations have been m a d e with numerous pure isomers and close-cut fractions (2-, 3-, or 4isomers) and form the basis of this report. Materials examined included a t least one individual isomer of each chain length from decyl through hexadecyl. As with the commercial mixtures, each pure compound was completely characterized via mass spectrometry, ;and then sulfonated and evaluated in a product formula. T h e synthetic work involved in the preparation of the pure isomers followed conventional routes. M a n y of the compounds were m a d e in these laboratories and included most of those reported on in 1955 by Gray, Gerecht, and Krems ( 7 ) and subsequent syntheses. Several other pure samples were
Present address, CoLgate-Palmolive Research Center, h-ew Brunswick, N. J.
obtained from outside laboratories, with the purity being established (or verified) in all instances. Some of the close-cut fractions were prepared \vithin our laboratories, to fill the gaps in the series otherwise obtained from outside sources. Initiallv, isomeric mixtures ivere made by alkylating benzene Lvith the appropriate I-n-olefin, producing a mixture of isomers dependent on the catalyst employed. T h e observed phenyl distributions for each catalyst (HF, AlCl,, and HzS04) parallel those described by Olson (2). Narrow-cut isomer fractions were subsequently prepared by careful fractional distillation of these reaction mixtures. T h e 5-, 6-, and 7-phenyl (internal) isomers made u p the lower boiling fraction, and commonly r a n about 90% in these isomers. T h e highest boiling fraction was essentially 2-phenyl isomer, being 95% or better in that isomer. Evaluation Techniques
All alkylbenzenes were sulfonated via standard procedures, with the resultant neutralized slurries being roll-dried to about ’90% active ingredient. A standard ABS was prepared in a comparable manner, and was used as the reference point in all evaluations. T h e ABS was a “tridecylbenzene” ( 3 ) . The typical heavy-duty detergent formulation consisted of 20 to 2576 active ingredient. 35 to 40% sodium tripolyphosphate, 5 to 1070 sodium orthosilicate, 25 to 30% sodium sulfate. and 5 to 10% moisture. T h e light-duty formulation was 30 to 35% active, 65 to ?O% sodium sulfate, and 1 to 2% moisture. The performance criteria of detergency and foam stability were examined in the heavy-duty case, Lvhile significant (though incomplete) foam stability studies in light-dut formulas were also studied. Detergency \vas measured by the change in reflectance following Xvashing in a Terg-0-Tometer. Standard soiled cotton swatches: U. S. Testing and Test Fabrics: were employed with customary measuring procedures. I n addition, tivo “natural soil” methods were used, each of which has been reported (5, 7). Foam stability was also evaluated with a battery of tests made u p of simulated and actual procedures. These methods included practical dishwashing ( 6 ) , simulated dishwashing ( J ) , dynamic sebum foam ( 4 ) ,and practical laundry washing VOL. 4
NO. 1
MARCH 1965
33
Table I.
Dishwashing Performance of 2-Phenyl Isomers in a Heavy-Duty Formulation LAS Plates iVashPd: ABS Isomer 50 p .p .m . 750p.p.m.
2-Phenyl 2-Phenyl 2-Phenyl 2-Phenyl 2-Phenyl 2-Phenyl 2-Phenyl
Clo CII Ci2 C13 Clr C15 Cia
0.05 0.05 0.46 0.70 0.65 0.15 0.05
Table II.
Heavy-Duty. The results for pure phenyl isomers in the decyl- through hexadecylbenzene series shoived that the foam stability of these LAS materials is dependent on the two variables of structure-namely, carbon chain length and phenyl position. T h e results in Table I for the 2-phenyl isomers show peak dishwashing performance in the C13 and C14 chain lengths. I t is particularly significant that these peak values are substantially below the standard ABS performance, being about 75% of standard at both hardnesses. Work with the homologous series of internal isomers again showed peak performers at Ci3 and C14 for SO p.p.m.. and C12 and C13 for 150 p.p.m. These data are shoivn in Table
A R.7
50p.p.m.
75Op.p.m
Internal C I O Internal C11 6-Phenyl Clr Internal C13 6-Phenyl C I A Internal C l i
0.05 0.05 0.93 1.27 1.15 0.96
0.15 0.25 1.30 1.10 0.90 0.50
Variations in Performancea with Skeletal Structure Plates Ilhshed. LAS ABS 50 7 50 p . p .m . p .p. ?n. ~~
Isonier
2-Phenyl C1.{ 4-Phenyl C i 3 6-Phenyl CIS
0 70
3-Phenyl 4-Phenyl 5-Phenyl 6-Phenyl 7-Phenyl
CI,
0.68
Clr
0.70
Clr Clt Clr
0.90 1.15 1.00
0.87 1.27
RI
R?
0.60 0.95 1.10
Methyl Propyl Pentyl
Undecyl Nonyl Heptyl
0.78 0.78 0.93 0.90 0.80
Ethyl Propvl Butyl Pentyl Hexyl
Undecyl Decyl Nonyl Octyl Heptyl
DishwashirrE prijormances in a heavy-duty formuintiori.
Table IV.
LAS Performances for Heavy-Duty Alkylates
Mass Spectral Characteristics of Three Coiniiiercial .%lkylates AlkylntP Xh .
1. 3243 2. 3211 3. 3796
11.
.2.fol. Wt.
.%fo/ar Distribution Cl? e 1 3 Cl, Clj
263 262 262
30 20 13
13 41 57
2-Pheny
28 8 0
15 30 29
25.7 30.2 22.8
Predicted and Observed Performances
T h e very important difference from the 2-phenyl isomers, however, was the tremendously beneficial performance exhibited in surpassing the performance of the standard ABS. Performances of the intermediate positions nominally fall between the indicated values of the 2- and internal isomers. Further, they can be approximated nicely from their closest homolog-e.g., .?-phenyl Clr is slightly better than 2-phenyl Cle but much poorer than 6-phenyl CIZ. Some of the performances of the intermediate-i.e., 3-, 4- and 5- -position isomers are presented in Table 111. I n several instances an isomer of one chain length had an exactly corresponding performer a t the next higher chain length but xvith a different phenyl position. For example. 4-phenyl C13 has virtually the same foam profile as 5-phenyl C I 4 and is substantially better than the 4-phenyl (214. T h e 4-phenyl C13 and 5-phenyl C14 have a C gside chain. While no rigorous generalization has been derived, it has been observed that the best foam performers are those with 12 to 15 total alkyl carbons, and propyl to hexyl (R,) and hexyl to nonyl (Rp) in the skeletal formula to the alkylbenzene as illustrated in Table 111. It has been reported (3) that for mixed chain and mixed isomer alkylates, the mass spectral analysis can be used to predict the observed performance. A direct relationship was established between foam stability characteristics and the observed amount of 5- and 6-phenyl isomers present, with appropriate formulas being given. Utilizing the data from 34
-
Isomer
Table 111.
Discussion and Results
LAS
Plates lthshed:
0.05 0.15 0.45 0.60 0.78 0.10 0.05
machine foam tests. Ordinarily, any one of these tests is sufficient to judge the approximate results for each of the others. Conditions for the practical dishwashing tests were 0.15% product concentration. at 115' F., and a t SO- and 150-p.p.m. water hardnesses, \vith a soil of hydrogenated vegetable oil. Under these test conditions, the standard .4BS washed 20 plates a t each hardness. T h e pure and narro\v-cut LAS materials were run in a statistically designed fashion, their performances being recorded as the ratio of the plates washed with the LAS to those m.ashed n i t h the standard ABS (concurrcntly).
Dishwashing Performance of Internal Isomers in a Heavy-Duty Formulation
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
Plates Mhshed:
L'4S ,4BS 750 P. P. .if. Pred. 0bsd~
~~~
50 P. P. X . Pred. Obsd.
1. 3243 3309 3156 3558 3308 3557 3362 3556 3423 3287 3626 3428 3632 3255
0.588 0.652 0.685 0.647 0.692 0.715 0.724 0.722 0.736 0.696 0.730 0.756 0.730 0 666
0.545 0.579 0.632 0.650 0.650 0.675 0.683 0.700 0.700 0.707 0.711 0,732 0.740 0.750
0.682 0,728 0.748 0.755 0.761 0.787 0.792 0.772 0.803 0.765
2.
321 1 3200 3420 3544 3561 3613 3559 3643 3560 3546 3667 3555
0.758 0,705 0.732 0.691 0.794 0.782 0.804 0.796 0.833 0.851 0.822 0.926
0 750
0.900
0.821 0,785 0.799 0.758 0.818 0.851 0.822 0,851 0.833 0.846 0,883 0.913
3796 3554
0.959 1.062
0,947 1.150
1.016 0,900
3.
0,757 0,757 0.780 0.804 0.818 0.828 0.829 0,849 0.865 0,881
0,796
0.817 0,795 0.739
0,629 0,700 0,675 0.775 0.789 0.775 0.833 0.775 0.763 0.762 0.738 0,786 0,840 0,732 0.840 0.763 0,829
0.790 0.808 0.795 0.813 0.881 0.821 0,805 0.953 0.925 1.023 0.900
~~
Table V. 0
Isomer
Sebum Foam at 150 P.P.M. Sebum Soil Added, .Wg. ~ _ 200 300 400 500 SO0 700 Foam heieht. inches
I.,
2-Phenvl Ci,
1
3-Phenyl C l r 4-Phenyl Cl4 5-Phenyl Clr 6-Phenyl Ci, Standard ABS
1 1 l'/, l'/i
1'1, 11/8
Ill,
Table VI.
1
'/?
.,
,
31,
,
.,
1"s 1'Is
1
l'/s
ll/,s lli~
1
.. 3's
1'/,
I]/$
l'/s
1
71s
..
LAS Heavy-Duty Detergency" Final Rfjectance Value 5Op.p.m. 7 50 p.p.ni.
Isomer Standard ABS 40,8 42.3 6-Phenyl CI:! 41 . 2 41.6 2-Phenyl C I , 42.0 42.9 2-Phenyl CI, 42 1 42.3 2-Phenyl CI:I 43.3 44.1 6-Phenyl C I , 43.9 44.3 6-Phenyl C I S 44.3 45.0 7-Phenyl C1, 45.2 45.9 Conditions: Test Fabrics. 0. 7,55:, concn.. 720' F., Ter,y-O- TonieiPr.
Table VII.
Dishwashing Performance of light-Duty Formulation
Isomers in a
Plates Ilhshed: IJonier
2-Phenyl GI,, 2-Phenyl Cll 2-Phenyl CI? 2-Phenyl CI:# 2-Phenyl CI, 2-Phenyl Cl, Internal ' 2 1 , Internal C I I 6-Phenyl CI, Internal CIS 6-Phenyl C1, Internal C I S
LA9 2 ABS --*
-
50 p .p .m .
7 i O p.p.m.
0.60 0.92 0.92 0.87 0.07 0.04 0.40 0.92 1.33 1 .07 0.78 0.26
0.64 0.96 0.50 0.14 0.07 0.04 0.64 0.96 1.22 0.88 0.26 0.05
the work reported here: a significant refinement in predicting performance has been m a d e through the development of individual performance constants for each chain and each isomer. Coupling these performance constants \\-ith the molar distribution a n d phenyl position analysis for a linear alkylate raw material, one can very rapidly a n d accurately predict its ultimate performance as a sulfonate. T a b l e IV is illustrative of some of the commercial linear alkylates t h a t have been pre-evaluated by this technique. T h e over-all correspondence between the predicted a n d observed performances holds for ividely diverse chain a n d isomer mixtures, a n d commonly agrees \vithin one-half a plate. A feir examples of the variety of raw materials being characterized are also presented in Table IV. All of the d a t a thus far have been determined via the prac-
tical dishwashing foam test. Essentially the same foam patterns were generated via the dynamic sebum foam test for _ the individual LAS materials. T a b l e V summarizes the sebum foam d a t a for the isomers depicted in T a b l e 111. Insufficient 7-phenyl tetradecane sulfonate was available to permit performing of the sebum foam tests with this material. T h e detergency studies of heavy-duty formulations \vere equally informative. I t has been reported ( 7 ) that detergency decreases as the phenyl group is moved from the 2 to the 5 position o n the straight-chain dodecylbenzene series. This has been confirmed, \vith the additional observation that the exact converse is true for the tridecyl- and tetradecylbenzene series. I n these t\vo series, the internal isomers are both superior detergents a n d foamers. D a t a for several of the dodecyl-, tridecyl-, and tetradecylbenzenes are presented in Table \'I. It'hile these d a t a were for Test Fabric soiled cloth, similar results \cere obtained for C . S.Testing cloths, a n d the txvo "natural soil" detergency tests. Table VI also shows that the effect of hardness on detersive porver is much more pronounced \vith the ABS t h a n with L.4S materials. Light-Duty. I n a manner completely analogous to the studies on heavy-duty systems? the performance of unbuilt light-duty detergent formulations \vas found to depend o n carbon chain distribution a n d phenyl position isomers. T h e optimum chain lengths of C1?to C14 for heavy-duty detergents have been shifted for the light-duty systems to the to range. T h e partial d a t a derived for light-duty formulations are shown in 'Table \ T I . Even these limited d a t a sho\v t h a t hardness has a pronounced effect o n the performance properties of individual isomers. T h e detailed examination of unbuilt systems and combined LAS-alkyl ether sulfate a n d LAS-nonionics and subsequent correlations are to form a separate communication. Acknowledgment
\Ye are indebted to Monsaqto Co., Oronite Chemicdl Co., a n d C n i o n Carbide's Olefins Division for many of the pure compounds reported on here. T h e samples prepared within our compan) u e r e largely joint efforts of our organic synthesis group. T h e Chemical Products Division a n d Analytical Section are also thanked. a n d individual contributions of V.J. Richter, I Y . G. Spangler. R . Anstett. L. Levinsky. and S. \Y. Babulak are gratefiilly recogniied. literature Cited
(1) G ~ a yF. , S.. Gerecht, .J. F., Krems, I. J., J . Or?. Chrm. 20, 511 (1933). ( 2 ) Olson. A . C.: Ind. En?. Chem. 5 2 , 833 (1960). (3) Kubinfeld, Joseph, Emery. E. M., Cross, H. D.. J . Ani. Oil Chemists' Sac. 41, 822 (1964). (4) Spangler, \V. G.. Zbid., 41, 300 (1964). (5) Spangler, \I,. G.. Cross: H. D., Schaafsnia. B. K., American Oil Chemists' Society Meeting. Oct. 11-14, 1964, Chicago. (6) Spangler, \V. G., Frantz, i\. J.. Buck, C. E.: AST.M D-12 Subcommittee on Detergents. March 10. 1959, New York. ( 7 ) Trowbridge. J. R.. Kubinfeld, J.: Fourth International Congress on Surface .Acti\.e Substances: Brussels, Belgium, Sept. 7-12. 1964. RECEIVED for review September 24: 1964 XCCEPTED December 31, 1964 Division of Industrial and Engineering Chemistry. 148th Meeting, .\CS. Chicago, Ill., September 1964.
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