Ind. Eng. Chem. Res. 1990, 29, 642-647
642
Amberlyst-15t-Catalyzed Alkylation of Phenolics with Branched Alkenes. Rearrangement of tert -Alkylphenols and Catechols to sec -Alkyl Isomers Curt B. Campbell, Anatoli Onopchenko,* and Donald C. Young Chevron Research Company, Richmond, California 94802
Alkylation of phenol or catechol with olefins capable of forming tert-alkylcarbonium ions, catalyzed via sulfonated cation-exchange resin (Amberlyst-E), gave the corresponding tert-alkylphenols at 25-130 O C , with higher temperatures favoring the para isomer. Alkylations at 140-150 " C , unexpectedly, gave sec-alkylphenols, with both ortho and para isomers being formed in almost equal amounts. The driving force of the reaction a t higher temperatures appears t o be the low stability of tert-alkylphenols, leading to reversibility of the alkylation reaction and subsequent formation of thermodynamically more stable sec-alkylphenols. The rearrangement of tert-alkylphenols t o sec-alkylphenols is favored when the tert-alkyl substituent is larger than tert-butyl. A paper by Olah et al. (1987) on the Nafion-H-catalyzed de-tert-butylation of aromatic compounds prompts us to report on the closely related alkylation of phenol and catechol with branched olefins (R2C=CH2or R2C=CHR) and the subsequent rearrangement of tert-alkylphenols to sec-alkylphenols. Branched olefins were used to increase the para content of alkylphenols and the 4-isomer content of alkylcatechols. The p-alkylphenol isomer imparts improved performance properties to the class of metallic detergents used in lubricating oils, known as phenates (Liston, 1988), and maximizing the 4-alkylcatechol isomer relative to 3-alkylcatechol overcomes toxicological problems associated with the biologically active 3-alkylcatechols (Baer et al., 1968, 1970; Billets et al., 1976; Corbett and Billets, 1975; Kurtz and Dawson, 1971). The most pertinent examples in the literature on the reaction of phenolics with branched species are limited to C4 systems (olefins, alcohols, halides) and propylene oligomers (C9,CI2) (Patinkin and Friedman, 1964; Reed, 1978; Rosenwald, 1978; Roberts and Khalaf, 1984). In the former examples, the tert-butylphenols produced do not isomerize into sec-butylphenols (Roberts and Khalaf, 1984; Saunders et al., 1968). In the latter examples, the products are extremely complex, and the sec-alkyl isomers are difficult to detect and have generally been overlooked. Considering that in 1988 alone over 370 X lo6 lb of nonyl- and dodecylphenols were produced in the US. by alkylation (Stanford Research Institute, 19881, our work with model branched olefins is important in that it sheds new light on the understanding of the chemistry involved, and this could lead to development of new, and more selective, alkylation processes. To get insight into the novel rearrangement occurring during alkylation, the rearrangement of neat p-(2methyl-2-undecy1)phenol was studied over commercial Amberlyst- 15 catalyst.
Results and Discussion Alkylation Reaction. The alkylation of phenol with propylene tetramer using Amberlyst-15 catalyst at 135 "C affords a product containing 90% p - and 10% o-dodecylphenols (IR) (Shrewsbury, 1960) at -80% olefin conversion. The highly hindered olefins in the tetramer feed remain unreacted even on further heating. These
* Author to whom
correspondence should be addressed. Amberlyst-15 is a registered trademark of Rohm and Haas Company.
Table I. Alkylation of Aromatics with 2-Butyl-l-octenen product isomer distribution, rxn olefin, % (GLC) substrate temp, "C time, h % convsn ortho para phenol 25 18 41 41.56 58.5* 75 2 93 16.36 83.76 100 1 94 6.0b 94.0b 51.5' 48.5c 145 3 95 23 70 36.Ib 63.3b 40 2 92 45.4c 54.6c 145d anisole 25 72 14 17.3b 82.T6 2 17 5.0b 95.0b 100 "Amberlyst-15, 1 g; olefin, 1 g; substrate, 3-5.6 g; n-decane or chlorobenzene solvent, -55 mL; atmospheric pressure, under N8. Single peak by GLC. Multiple peaks by GLC; composition determined by infrared spectroscopy. dContinue 40 O C run at 145 "C.
results are consistent with the literature reports and with the results from commercial processes using similar reaction conditions and catalysts (Rajadhyaksha and Chaudhari, 1988; Rosenwald, 1978; Reed, 1978). When the above alkylation reaction is carried out a t 150 "C (upper temperature limit of Amberlyst-15) (Huang and Yurchak, 1977), the para isomer content decreased to 70%, while the ortho increased to 30% (IR), even though the starting tetramer contained less than 20% linear olefins (NMR) (Kalabin et al., 1986). This observation is contrary to the report that ortho substitution can be controlled by use of a more active catalyst and more severe reaction conditions since ortho derivatives can undergo isomerization to their para form (Rosenwald, 1978). Further examination of the 150 "C product by NMR shows the ortho isomers to be mostly sec-dodecylphenols (6 3.0, PhCH) (30%)and the para isomers to be sec-dodecylphenols (6 2.5, PhCH) (18%) and tert-dodecylphenols (mostly para, 52% ) (Lindeman and Nicksic, 1964; Crutchfield et al., 1964). This analysis indicated to us that a significant rearrangement reaction was occurring at the higher temperature, but the product mixture was too complex for a detailed study. The present work was initiated to study the reaction of phenol and catechol with 2-butyl-1-octeneas a model olefin (Tables I and 11). Alkylations were carried out in a batch procedure using a large excess of phenol (phenol/olefin, 5-10/ 1 M) to minimize the formation of dialkylated products which complicate the analysis. Typically, high catalyst concentrations were used (Amberlyst-15,5-20% 1, and reactions were conveniently carried out in n-decane,
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0888-5885/90/2629-O642$O2.50/0 0 1990 American Chemical Society
Ind. Eng. Chem. Res., Vol. 29, No. 4, 1990 643 Table 11. Alkylation of Aromatics w i t h 2-Butyl-1-octene" product isomer distribution, temp, rxn olefin, % (GLC) substrate O C time. h YO convsn 3-alkvl 4-alkvl 0.5 66 catechol 85 3.4b 96.6b 0.5 75 1.6b 98.4b 105 145 3 92 45.6c 54.4c 1,2-dimethoxy- 100 4 10 1.0b 99.0b benzene o-xylene 120 4 62 7.5c 92.5c 150 3 95 9.8c 90.2c
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'Amberlyst-15, 1 g; olefin, 1 g; substrate, 3-4.5 g; n-decane or chlorobenzene solvent, -55 mL; atmospheric pressure, under Nz. Single peak by GLC. Multiple peaks by GLC; composition determined by infrared spectroscopy. J
Chart I
I
3.2 OH
1
I
3.0
2.8
I
I
1
I
2.6
I
2.4
I
2.2
Me
3-sec-Dodecyl
4-sec-Dodecyl
140-150'C
R2-C R3 H
chlorobenzene, or o-dichlorobenzene solvent (Chart I). Alkylation of phenol with 2-butyl- 1-octene between 25 and 130 "C affords the corresponding p - and o-tert-dodecylphenols, with the higher temperature favoring the para isomer (Table I). Between 120 and 130 "C, the para isomer comprised over 95% of the total product. The two peaks appearing on the GLC chromatogram were sharp, single peaks, suggesting the presence of one ortho isomer and one para isomer. When the reaction was attempted at 145 "C to prepare the para isomer exclusively, a complex mixture was obtained (GLC). Analysis by infrared spectroscopy (Shrewsbury, 1960) showed -30% ortho and -70% para isomers. The high-field NMR spectrum of the product suggested the presence of sec-alkylphenols on the basis of benzylic methine protons at 6 2.2-2.7 (para) and 6 2.7-3.2 (ortho), respectively (Figure 1). From the integration of methine and aromatic protons, it was estimated that about half the product consisted of sec-dodecylphenols (-60% ortho, -40% para) and half consisted of tert-dodecylphenols (by difference). Thus, most of the ortho isomers formed at elevated temperatures were accounted for as sec-alkyl-substituted phenols. Alkylation of phenol with 2-methyl-1-undecene at 150 "C gave similar results to those obtained with P-butyl-loctene above, although the rearrangement with the latter appeared more facile. Alkylation of catechol (Table 11) gave comparable results to those obtained with phenol, except that alkylations below 80 "C could not be run without the catechol crystallizing out of solution. Catechol was soluble in glyme at room temperature but gave no alkylation after 4 h at 50 "C. Anisole (Table I) and veratrole (1,2-dimethoxybenzene, Table 11) in the moderate temperature range behaved like the corresponding phenols, although they were of lower reactivity (Attine et al., 1976). In our work, we made no attempt to achieve complete rearrangement of tert-alkylphenols to sec-alkylphenols nor
3.2
3.0
2.8
2.6
2.4
2.2
ppm
Figure 1. 'H NMR spectra (300 MHz, ArCH region) of the product from the alkylation of phenol with 2-butyl-1-octene a t 145 O C (top), and sec-dodecylcatechols (bottom).
to find the optimum conditions for such a reaction, although higher operating temperatures and longer reaction times seemed to favor the formation of sec-alkylphenols. To help identify the products, high-field NMR spectra (300 MHz, ArCH region) of model sec-alkylcatechols were recorded (Figures 1 and 2); the spectra for the corresponding sec-alkylphenols were essentially identical. Comparing the spectra in Figures 1 and 2, it appears that the benzylic proton in (1-methylhepty1)- or (l-methylundecyl)catechol, for example, resonates further d o d i e l d , while in (1-ethylhexy1)- or (1-ethyldecy1)catechol it resonates further upfield, in both the 3- and the 4-alkylcatechols. To confirm this assignment, a lH-13C shiftcorrelated spectrum was obtained for sec-octylcatechols (Figure 3). The NMR results are in line with the above assignment and can be explained on the basis of known 0 effects. Rearrangement Reaction. To gain further insight into the novel rearrangement occurring during the alkylation of phenols, the reaction of neat p-(2-methyl-2-undecyl)phenol over Amberlyst-15 was studied. A t 150 "C, this phenolic has a half-life ( t l l z )of about 2 h. After 6 h, the product mixture consisted of isomerized alkylphenols (57%), dialkylphenols (29%),phenol (lo%), and dodecenes (4%) at -85% conversion (Chart 11). Analysis of the above product by GC/MS, concentrating on the monoalkylphenols, showed a t least 30 isomers, 14 of which accounted for over 90% of the total mass of alkylphenols. All dodecylphenol isomers showed weak
644 Ind. Eng. Chem. Res., Vol. 29, No. 4, 1990 3-sec-Hexyl
4-sec-Hexyl
I it
l
l
3.2
I
I
3.0
I
I
2.8
1
1
1
2.6
3-sec-Octyl
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2.4
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2.2
4-sec-Octyl
,
,
,
,
L
,
Q
chemical shift (ppm) Figure 4. lHJ3C shift-correlated spectrum (contour plot) of product from alkylation of phenol with 2-butyl-1-octene at 145 "C (ArCH region). C h a r t I1 CH
Ambarlyst- 15 (6 WI %I
w
w
w CH3-C-CH3
3.2
3.0
2.8
2.6
2.4
2.2
PPm
Figure 2. 'H NMR spectra (300 MHz, ArCH region) of sec-hexylcatechols (top) and sec-octylcatechols (bottom).
49%
I
CQh9
L 30%
'H chemical shift (ppm) Figure 3. 1H-13C shift-correlated spectrum (contour plot) of secoctylcatechols (aliphatic proton region).
parent ions at mlz 262 and base ions at m l z 107,121,135, or 149. These base ions are ascribed to hydroxytropylium, or their equivalent hydroxybenzyl ions, formed by a loss of the longer alkyl group a t the point of branching from the parent ion and in some cases followed by loss of an
alkene. The m / z 107 base ion is ascribed to an ion formed by the fragmentation of either a primary-substituted phenol or a secondary-substituted phenol in which the alkyl groups on the benzylic carbon or ethyl or longer. The mlz 121 ion is ascribed to the ion formed by the fragmentation of a secondary-substituted phenol containing a single methyl group at the benzylic carbon and the m/z 135 ion to the tropylium ion formed by fragmentation of a tertiary-substituted alkylphenol containing two methyl groups at the benzylic carbon. The mlz 149 ion is assigned to the homologous m / z 135 ion. The various patterns that were useful in determining the structures of alkylphenols by mass spectrometry are available (Meyerson and Hart, 1963). One of the surprising findings from the mass spectral work was the detection of a small amount of primary substitution product (ArCH2R,
