Energy & Fuels 1990,4, 538-543
538
Products a and q can give rise to P-cleavage products d and t as shown. Scheme I1 explains the formation of benzofurans and xanthenes. The ortho-alkylated phenol A forms the radical B which can lose R' to give the ortho-quinonoid structure C. C can tautomerize to give vinylphenol D. D can either cyclize to give benzofuran F via E or react with B to give xanthene H via G.
Scheme I1
i F
E
4. ""::" \
o
'
R
H
R
\
O0
H R G
quinonoid forms undergo either water addition (to give h or n) or isomerization (into a or 9). Products h and n cleave to give phenol (k)and carbonyl compounds i and 0, which can react again with phenol (or alkylphenols) to give o-(0-hydroxyalky1)-substituted phenols j and p, which can undergo reduction to the o-alkylphenols e and v.
Conclusions Forcing Bucherer reaction conditions with various 4alkyl-substituted phenols led mainly to dealkylation. By changing the nature of the 4-substituent, from primary to quaternary (methyl to tert-butyl), it was found that the dealkylations occur via an oxidative pathway. Under similar treatment with sulfite/ bisulfite mixtures, phenols with a-oxygenated 4-substituents (Le., 4hydroxyacetophenone, 4-hydroxybenzaldehyde, and 4hydroxybenzoic acid) readily lost the substituent to give phenol as the only major product. Phenols with long alkyl chain substituents at the 4-position lost their alkyl chains. The structures of the products formed from a variety of 4-substituted phenols are determined and reaction pathways for their formation are proposed. The basic reaction paths include dealkylation, alkylation, and ring closure. Supplementary Material Available: Table I1 listing properties and mass spectral data of starting materials and Table I11 comparing experimental and literature mass spectral fragmentation data of products (4 pages). Ordering information is given on any current masthead page.
Aqueous High-Temperature Chemistry of Carbo- and Heterocycles. 9.' Aquathermolysis of Ortho-Substituted, Meta-Substituted, and Multisubstituted Phenols in the Presence and Absence of Sodium Bisulfite Alan R. Katritzky* and Ramiah Murugan Department of Chemistry, University of Florida, Gainesville, Florida 32611 -2046
Michael Siskin* Corporate Research Science Laboratory, Exxon Research and Engineering Company, Annandale, New Jersey 08801 Received December 13, 1989. Revised Manuscript Received April 14, 1990
Aquathermolyses, with or without the addition of the Bucherer reagents, were studied for 0-and m-cresol and 2-ethyl-, 2-isopropyl-, 2,4,6-trimethyl-, and 3,4,5-trimethylphenols. Ortho and para, but not meta, alkyl groups in the phenols are attacked readily by NaHS03 with loss or conversion to lower alkyl groups. o-Ethyl- and isopropylphenols are converted after short reaction times into benzofurans, but on longer heating, the furan rings are reopened to give degradation of, or complete loss of, the original o-alkyl groups. Introduction Part 8 of this series discussed the reactions of various 4-substituted phenols. The present paper extends this (1) For part 8 in fi =e: A. R.;M - ~ , M. Energy Fuels, preceding paper in this issue.
R.;Siskin,
0887-0624/90/2504-0538$02.50/0
work to some ortho- and meta-substituted phenols and also to polysubstituted phenols*' Experimental Section The gas chromatographic behavior of all the compounds encountered in this work (starting materials and products) is summarized in Table I. Table II records the source and ma99 spectral 0 1990 American Chemical Society
Energy & Fuels, Vol. 4, No. 5, 1990 539
Aquathermolysis of Carbo- and Heterocycles. 9
t?
no. 1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
41 42 a See
min 0.40 0.43 0.44 1.05 1.64 1.99 2.10 2.69 3.00 3.01 3.16 3.30 3.71 3.75 3.78 4.07 4.33 4.43 4.48 4.64 4.70 4.85 4.91 5.28 5.30 5.87 5.99 7.11 7.45 11.79 13.92 14.67 15.06 15.50 15.52 15.62 16.15 16.24 16.38 16.50 16.75 17.60
Table I. Structure and Identification of Starting Materials mol wt structurea 84 4,5-dihydro-3-methylfuran 68 furan 96 2,5-dimethylfuran 106 m-xylene 110 thiophenol 94 phenol 118 benzofuran 108 o-cresol 108 p-cresol 108 m-cresol 132 3-methylbenzofuran 122 2,4-dimethylphenol 122 2-ethylphenol 136 2-hydroxyacetophenone 122 2,6-dimethylphenol 122 3,4-dimethylphenol 134 3-hydroxybenzofuran 136 2-isopropylphenol 122 3,5-dimethylphenol 136 2,4,64rimethylphenol 146 3,5-dimethylbenzofuran 148 3-methylbenzofuran-2(3H)-one 136 4-isopropylphenol 136 2,4,5-trimethylphenol 154 3-methyl-l-(thiomethyl)phenol 136 3,4,5-trimethylphenol 164 4-ethyl-2-isopropylphenol 150 2,3,4,5-tetramethylphenol 164 5-ethyl-2-hydroxyacetophenone 210 2,7-dimethylxanthene 242 3,3’-diethyL4,4’-dihydroxybiphenyl 242 3,3’-diethyl-2,4’-dihydroxybiphenyl 270 2,2’-dihydroxy-4,4’5,5’,6,6’-hexamethylbiphenyl 270 4,4’-dihydroxy-3,3’-diisopropylbiphenyl 242 3,3’-diethyl-2,2’-dihydroxybiphenyl 270 2,2’,4,4’,6,6’-hexamethyl-2,2’-bicyclohexadienone 270 2,2’,4,4‘,6,6’-hexamethyl-2,4’bicyclohexadienone 270 2,4’-dihydroxy-3,3’,5-triethylbiphenyl 270 2,2’-dihydroxy-3,3’,5-triethylbiphenyl 270 2,2’,4,4’,6,6’-hexamethyl-4,4’bicyclohexadienone 252 4,5-diethylxanthone 2- (3,5-dimethyl-2-hydroxyphenyl)-5,7-dimethylbenzofuran 266
and Products identification equiv basis wt 84 Table I11 Table I11 68 Table I11 96 Table I11 106 110 Table I1 Table I1 94 Table I11 118 Table I1 108 108 Table I1 Table I1 108 Table I11 132 122 Table I11 Table I1 122 Table I11 136 Table I11 122 122 Table I11 Table I11 134 Table I1 136 Table I11 122 Table I1 136 Table IV 146 Table I11 148 Table I1 136 Table I11 136 Table I11 154 Table I1 136 Table IV 164 Table IV 150 Table IV 164 Table IV 105 Table IV 121 Table IV 121 Table IV 135 Table IV 135 121 Table IV Table IV 135 Table IV 135 Table IV 135 Table IV 135 Table IV 135 Table IV 126 Table IV 133
response factor 0.78 0.77 0.96 0.72 0.76 0.76 0.79 0.77 0.77 0.75 0.78 0.78 0.60 0.78 0.78 0.59 0.77 0.78 0.75 0.75 0.58 0.78 0.77 0.53 0.77 0.76 0.77 0.59 0.73 0.56 0.56 0.55 0.55 0.56 0.55 0.55 0.55 0.55 0.55 0.55 0.53
Chart I for the structures of these compounds.
Table IV. Identification of Products from Mass Spectral Fragmentation Patterns no. compound“ MW fragmentation pattern, m/z (% relative intensity, structure of fragment ion) 146 146 (100, M); 131 (75, M - CH3); 115 (30, 131 - 0);91 (10, C7H7) 21 3,5-(Me)2-benzofuran 164 164 (100, M); 135 (35, M - C2H5); 121 (20, 135 - CH2); 108 (10, M - C4Hs); 91 (30, C7H7) 27 4-Et-2-i-Pr-phenol 150 150 (60, M);135 (100, M - CH3); 121 (60, 135 - CH& 107 (30, 121 - CHz); 91 (50,C7H7) 28 2,3,4,5-(Me),-phenol 164 164 (25, M); 149 (100, M - CH3); 121 (15, 149 - CO); 91 (40, C7H7); 77 (35, C6H.5) 29 5-Et-2-HO-acetophenone 210 210 (70, M); 209 (100, M - H); 195 (65, M - CH3); 165 (15, 195 - CHZO); 104 (40, M 30 3,6-(Me)z-xanthene C&.C&o) 242 242 (40, M);227 (100, M - CHJ; 213 (60, M - CZH,); 212 (40, 227 - CH3); 121 (75, M 31 3,3’-(Et&4,4’-(OH),-biphenyl CzH&H40) 242 242 (100, M); 227 (70, M - CHJ; 213 (30, M - CZH5); 115 (60, M - C2H&H,O2); 77 (40, 32 3,3’-(Et)z-2,4’-(OH)n-biphenyl C6H5)
33 34 35
36 37
38 39 40
41 42
270 270 (100. M): 255 (50. M - CHd: 240 (10. 255 - CHd: 225 (10.240 - CHd: 135 (20. M OC&(CH3)3) 270 270 (100, M); 225 (70, M - CH3); 240 (40, 255 - CH3); 227 (20, M - CH(CH3)z); 135 (25, M - OCeH,CH(CH,)o) 242 242 (50, Mj; $27 (40, M - CH,); 213 (20, M - C2HJ; 121 (40, M - C2H5C6H3OH); 77 (100, CBHd 270 270 (75, M);135 (100, M - C,jHz(CHs)30); 121 (40, 135 - CH2); 105 (30, 121 - 0);91 (90, C7H7) 270 270 (100,M); 255 (10,M - CHJ; 240 (5, 255 - CHs); 225 (5,240 - CH3); 135 (70, M C&z(CH&@) 270 270 (75, M); 255 (100, M - CH3); 242 (80, M - CZH,); 227 (70, 242 - CH3); 91 (60, C7H7) 270 270 (25. M): 255 (100. M - CH.): 242 (50. M - &HA): 227 (40. 242 - CHd: 77 (40. CsHd 270 270 (lob, M);255 (20; M - CH& 148 (80; M - C,H;(CHJzOH); 135 (90,”MCBHz(CH3)sO); 120 (20, 135 - CH3) 252 252 (100, M); 237 (80, M - CH,); 223 (20, M - CzH.5); 165 (60, 223 - CO, C2H51 266 266 (100, M); 251 (10, M - CHJ; 237 (10, 251 - CH2); 223 (20, 237 - CHJ
Osee Chart I for the structures of these compounds.
.
I
”
Katritzky et al.
540 Energy & Fuels, Vol. 4, No. 5, 1990 Chart I
2
1
19
3
4
21
CHI 20
30
OH HO
CHI
5
6
Q
22
31
32
34
3s
(11, 24
/
CHI CHI
33
HICl
,OH
,C>IL
H S/?
38
fragmentation data of the authentic compounds used, either as starting materials or for the identification of products. Tables I11 and IV record the mass spectral fragmentation patterns of products for which authentic samples were not available and which were identified by comparison with literature MS data (Table 111) or by deduction (Table IV). The aquathermolyses were conducted as previously described: and the results are collected in Table V onward. Tables I1 and I11 have been deposited as supplementary material (see paragraph at end of paper regarding supplementary material).
Mass Spectral Assignments of Structures The final structures for the compounds listed in Table IV were deduced by considering the fragmentation pat(2) Katritzky, A. R.; Lapucha, A.; Murugan, R.; Luxem, F.; Siskin, M.; Brons, G. Energy Fuels, part 1, in this issue.
terns, the reaction conditions, and reasonable mechanistic pathways (e.g., oxidative coupling of phenols) from the starting materials. Five different types of products are seen in these reactions: (i) alkylphenols 27 and 28, (ii) acetophenone derivative 29, (iii) benzofurans 21 and 42, (iv) xanthene derivatives 30 and 41, and (v) biphenyl derivatives 31-40. The biphenyl derivatives are assumed to be formed by mechanisms similar to that of the oxidative coupling of phenols3 (where C-C coupling of phenolic radicals occurs at the ortho or para positions). Products i were observed both under Bucherer and non-Bucherer reaction conditions, whereas products of types ii, iii, and iv were observed only in the presence of bisulfite and products v were seen only in the absence of bisulfite. The alkylphenols of type i, 2-isopropyl-4-ethylphenol (27) and 2,3,4,5-tetramethylphenol (28), are easily identified from their fragmentation patterns, which are similar to those for other alkylphenols, and from the differences in M+ from the starting materials, which are in multiples of 14. The mass spectrum of phenol itself shows major loss of 28 (CO) and 29 (CHO) mass units. For cresols, there is a major loss of 1(H) unit. However, for dimethylphenols the loss of 15 (CHJ units is predominant. The M - 28 and M - 29 ions, so important in phenol, are greatly reduced in methylated phenols, and peaks corresponding to the loss of 18 (H,O) units become noticeable. Phenols with long saturated chains, like alkylbenzenes, show simple benzylic cleavage in addition to the usual McLafferty rearrangement~.~ This, along with comparisons of the retention times with different alkylphenols, provides evidence for their structures. 5-Ethyl-2-hydroxyacetophenone (29). The MS fragmentation shows the loss of 15 (CHJ and 28 (CO) units, which is similar to that observed for a~etophenone.~It was identified as an alkylphenol from the broad appearance of the GC peak, and the structure 29 was assigned on the basis of its molecular weight and its production from o-ethylphenol. The benzofurans 21 and 42 were identified from their fragmentation patterns which were similar to other benzofuran@ and the formation of other directly identified known benzofurans 11, 17,21, and 22 as products in the Bucherer type reactions. Benzofuran itself shows major loss of 28 (CO) and 29 (CHO) units. For alkylbenzofurans the @-cleavageis preferred when the alkyl group is at position 2, 3, 4,or 7.6 The xanthenes 30 and 41 were assigned from their fragmentation patterns, which were similar to other xanthene derivatives7 The ready loss of hydrogen from the M+ of 30 and a ready loss of CO from 41 are characteristic of these compounds. The mass spectrum of xanthone showed the expected loss of 28 units (CO). However, this M - 28 ion further fragmented with a loss of 28 units The latter fragmentation was similar (CO) and 1 unit (H). to that for dibenzofuran i t ~ e l f . ~F o r fragmentation of xanthene, see Table I11 of part 8 of this series.' The biphenyls 31-40 were identified mainly from the M+, which were usually double the M+ of the starting (3) Barton, D.; Ollis, W. D. Comprehensive Organic Chemistry; Stoddart, J. F., Ed.; Pergamon Press: Oxford, 1979;Vol. 1, 746. (4) Budzikiewicz, H.; Djerassi, C.; Williams, D. H. Mass Spectrometry of Organic Compounds; Holden-Day: San Francisco, 1967;p 115. (5) Meyerson, S.;Rylander, P. N. J . Am. Chem. SOC.1957, 79,1058. (6)Porter, Q. N.; Baldas, J. Mass Spectrometry of Heterocyclic Compounds; Wiley Interscience: New York, 1971; p 131. Willhalm, B.; Thomas, A. F.; Gautschi, F. Tetrahedron 1964,20, 1185. (7)Barnes, C. S.;Occolowitz, J. L. Aust. J. Chem. 1964, 17, 975. Cheshire, M.V.;Cranwell, P. A.; Falshaw, C. P.; Floyd, A. J.; Haworth, R. D. Tetrahedron 1967, 23, 1669.
Energy & Fuels, Vol. 4, No. 5, 1990 541
Aquathermolysis of Carbo- and Heterocycles. 9
Table V. Products of 0-Cresol (8) and m-Cresol (10) Reactions
no.
compound solvent additive (10%) temp, "C time, h structure
6 8 9 10 15 19 30
phenol o-cresol p-cresol m-cresol 2,6-dimethylphenol 3,5-dimethylphenol 2,7-dimethylxanthene
c&2
250 72
99.6 0.4
o-MeC6H40H H2O aq NaHS03 (satd) Na2S03 250 250 264 264 0.2 99.4 0.4
CsHI2 250 72
m-MeC6H40H H20 aq NaHS03 (satd) Na2S03 250 250 264 264
9.8 89.6
0.3 0.1
100.0
99.5
100.0
0.3 0.1
0.3 Scheme I OH
c--
CHR' ___)
8
I OH
CH2R'
R
so 14,29
+ 35, 39 cross coupled products
R
+
cross coupled products
material or double plus 14 units. The orientations of the couplings that produced these compounds were assumed to be as found for different alkylphenols in the literature8 at the ortho-ortho, ortho-para, or para-para positions. In products from 2,4,6-trimethylphenol the biphenyl derivatives were considered to be cyclohexadienones, which is in line with literature reports of coupling of Cmethyl- and 2,6-dimethylphenols.@From an examination of the mass spectral fragmentation patterns of alkylphenols4 it was found that they behave in a way similar to alkylbenzenes, so it could be concluded that phenols behave similarly to biphenyls. Alkylated biphenyls show the same behavior as alkylbenzenes.'O Thus, by analogy to toluene the most
(8) Bacon, R. G. R.; Hill, H. A. 0. Q. Reo., Chem. SOC.1965,19,95. Scott, A. I. Ibid. 1965, 19, 1. (9) Chen, C. L.; Connors, W. J.; Shinker, W. M. J. Org. Chem. 1969, 34,2966.Schwartz, M. A.; Holton, R. A.; Scott, S. W. J. Am.Chem. SOC. 1969,92, 2800.
31,34
cross coupled products
important peak in the spectra of methylbiphenyls is due to the loss of 1unit (H), while 2-ethylbiphenylexhibits the expulsion both of 1 (H) and 15 (CH,) units.'O
Results and Discussion o- and m-Cresols (Table V). m-Cresol shows almost
no reaction in cyclohexane (250 OC/3 days) or water (250 OC/ll days) and in the sulfte/bisulfite mixture (250 OC/11 days) was only 0.5% converted to dealkylated or rearranged products, indicating the lack of reactivity of m-alkyl groups toward attack by Na$303/NaHS03 0-Cresol shows 10% conversion to phenol with traces of other products, but only under the most forcing conditions. 2-Ethyl- and 2-Isopropylphenol (Table VI). These show no significant reactions in cyclohexane and little in water, but far wide slates of reaction products under (10) Budzikiewicz, H.; Djerassi, C.; Williams, D. H. Mass Spectrometry of Organic Compounds; Holden-Day: San Francisco, 1967; p 86.
Katritzky et al.
542 Energy & Fuels, Vol. 4, No. 5, 1990
Table VI. Products of 2-Ethylphenol (13) and 2-Isopropylphenol (18) Reactions 2-Et-Dhenol 2-i-Pr-Dhenol compound CBH12 H 2 0 aq NaHSO, aq NaHS0, aq NaHSO, C6H12 H 2 0 aq NaHS03 aq NaHS0, solvent Na2S03 Na2S03 Na2S03 Na2S03 Na2S03 additive (10%) 250 250 250 250 250 250 250 250 250 temp, “C 14 72 72 72 13 84 110 72 72 time, h no. structure 1 2 3 6 7 8 11 13 14
17 18 21 22 23 25 27 29 31 32 34 35 38 39 41
0.6
4,5-dihydro-3-methylfuran furan 2,5-dimethylfuran phenol benzofuran o-cresol 3-methylbenzofuran 2-ethylphenol 2-hydroxyacetophenone 3-hydroxybenzofuran 24sopropylphenol 3,5-dimethylbenzofuran 3-Me-2-OH-benzofuran 4-isopropylphenol 4-SCH3-3-Me-phenol 4-Et-2-i-Pr-phenol 5-Et-2-HO-acetophenone
1.3 0.4
99.6 97.5
3,3’-(Et)2-4,4’-(OH)2-biphenyl 0.4 3,3’-(Et)2-2,4’-(OH)2-biphenyl 4,4’-(OH)2-3,3’-(i-Pr)2-biphenyl 3,3’-(Et)2-2,2’-(OH)2-biphenyl 2,4’-(0H)2-3,3’,5-(Et)3-biphenyl 2,2’-(OH)2-3,3’,5-(Et)3-biphenyl
7.1 2.1 0.7
60.8
72.2
34.3
26.5
75.0 1.5 2.6
4.9
0.6
100.0 97.8
1.3 56.8
8.6 4.1 30.6 2.5
37.0
41.7 6.8 4.2
1.8
3.1
0.3 1.3 1.4 1.1
0.8 0.7 0.4 0.4 0.5
4,5-diethylxanthone
2.5
Table VII. Products of 2,4,6-Trimethylphenol (20) and 3,4,5-Trimethylphenol (26) Reactions 2,4,6-(Me),-phenol 3,4,5-(Me),-phenol compound solvent C6H12 H 2 0 aq NaHSO, aq NaHS03 C6H12 H 2 0 aq NaHS0, aq NaHS0, additive (10%) Na2S03 Na2S03 Na2S03 Na2S03 250 250 250 250 250 250 250 250 temp, “C 72 48 13 56 72 48 14 56 time, h no. structure ~~
4 5 6 8 9 10 12 15 16 19 20 24 26 28 33 36 37 40 42
m-xylene thiophenol phenol cresol p-cresol m-cresol 2,4-dimethylphenol 2,6-dimethylphenol 3,4-dimethylphenol 3,5-dimethylphenol 2,4,6-trimethylphenol 2,4,5-trimethylphenol 3,4,5-trimethylphenol 2,3,4,5-tetramethylphenol
0.1
0.3
99.2
2,2’-(0H)2-4,4’,5,5’,6,6’-(Me)B-biphenyl 2,2’,4,4’,6,6’-(Me)6-2,2’-bicyclohexadienone 2,2’,4,4’,6,6‘-(Me)6-2,4’-bicyclohexadienone 2,2’,4,4’,6,6’-(Me)6-4,4‘-bicyclohexadienone 0.8 2-(3,5-(Me)2-2-OH-Ph)-5,7-(Me)2-benzofuran
94.3
5.2
4.0
16.0 9.8 0.5
17.0 10.4 0.2
68.5
Bucherer conditions. Long reaction times convert both compounds mainly into phenol and o-cresol. However, during short reaction times these compounds afford considerable quantities of benzofuran (7) and of 3-methylbenzofuran (11),respectively, presumably by ring closures of intermediates formed by a mechanism similar to that discussed for the corresponding para isomer in the preceding paper.‘ In addition, smaller quantities of other benzofurans 21 and 22 were observed. With water alone, small quantities of oxidatively coupled phenols were seen. Trimethylphenols (Table VII). The main reaction is demethylation to give 3,4-dimethylphenol in the sulfite mixture. Presumably, steric strain in the starting material increased the rate of 5-demethylation. Steric hindrance by the 3- and 5-methyl groups would reduce the rate of
3.0
0.6
1.0
36.8 1.9
49.7 2.5
99.4
93.8
4.6 51.7 3.0
4.1 38.5 1.6
62.8
1.0
0.8 0.5 4.0
2.0
5.2
2.2 2.4
4-demethylation so that only small amounts of 3,5-dimethylphenol are seen. Small amounts of phenols 10,24, and 28 result from dealkylations and/or alkylation. Predominant products from the Bucherer type reaction of 2,4,6-trimethylphenol are the expected 2,4- (12)and 2,6-dimethylphenols (15), along with small quantities of p-cresol (9). With water alone oxidatively coupled phenols (biphenols) were the major products from both 2,4,6- and 3,4,5-trimethylphenols. The proposed reaction pathways and mechanisms are similar to those given for para-substituted phenols in part 8 of this series. Specific pathways are detailed in Scheme I, which seeks to rationalize the formation of the observed products (other than trans-alkylation). The low reactivity of m-methyl groups is clearly rationalized by this
Energy & Fuels 1990,4, 543-546 scheme-the phenoxy radical can only interact directly with an 0- or p-alkyl group.
Conclusions 2-Alkyl groups Gust as previously found for 4-alkYl groups') Can be removed from alkYlPhenols with an aqueous sulfite mixture at high temperatures. When the o-alkyl group contains a t least two carbon atoms, benzo-
543
furans are formed as by-products. 3-Alkyl groups are relatively inert. Reactions in water without added sulfides give small quantities of oxidatively coupled biphenols. S u p p l e m e n t a r y Material Available: Table I1 listing properties and mass spectral data of starting materials and Table I11 comparing experimental and literature mass spectral fragmentation data of products (3 pages). Ordering information is given on any current masthead page.
Aqueous High-Temperature Chemistry of Carbo- and Heterocycles. 10.' Aquathermolysis of Acyclic and Cyclic Phenol Ethers in the Presence of Sodium Bisulfite or Phosphoric Acid Alan R. Katritzky,* Ramiah Murugan, and Marudai Balasubramanian Department of Chemistry, University of Florida, Gainesville, Florida 32611-2046
Michael Siskin* Corporate Research Science Laboratory, Exxon Research and Engineering Company, Annandale, New Jersey 08801 Received December 13, 1989. Revised Manuscript Received May 14, 1990
On aquathermolysis in a sulfite/bisulfite mixture, anisole and n-butyl phenyl ether show 27% and 19% cleavage conversion, respectively, with phenol as the only product. In 10% aqueous phosphoric acid, in addition to phenol, small amounts of alkylated products were also observed. When phenol was reacted with methanol or butanol in 10% phosphoric acid, the same slates of products were obtained as had been obtained from the corresponding ethers. As negligible conversions were seen in cyclohexane, acid-catalyzedionic mechanisms are proposed. 2,3-Dihydrobemofuran also gave phenol as the major product with some alkylphenols and dimers. Diphenyl ether showed no conversion under the conditions employed.
Introduction Ether bonds are one of the major cross-links present in coals and kerogens.*p3 The cleavage of ether cross-links in resources has immense potential for the synfuels industrya4p5 In this paper, we report an aquathermolytic study of cyclic and acyclic phenol ethers. This work is an extension of our studies on the use of Bucherer reaction conditions for the dealkylation of phenols1v6in which we have investigated the action of aqueous bisulfite/sulfite mixtures on the reactivity of phenolic ethers. For comparison, we also carried out our reactions in cyclohexane (to detect thermal reactions), in water (to differentiate aqueous reactions), and in 10% aqueous phosphoric acid (to monitor acid catalysis). (1) For part 9 of the series Aqueous High-Temperature Chemistry of Carbo- and Heterocycles, see: Katritzky, A. R.; Murugan, R.; Siskin, M. Energy Fuels, preceding paper in this issue. (2) Shinn, J. H. Fuel 1984, 63, 1187. (3) Scouten, C. G.; Siskin, M.; Rose, K. D.; Aczel, T.; Colgrove, S. G.; Pabst, R. E., Jr. Prep.-Am. Chem. Soc., Diu. Pet. Chem. 1989,34,43. (4) Glombitza, K.; Wolwer-Rieck, U. Liebigs Ann. Chem. 1988, 261. (5) Dewald, R. R.; Conlon, N. J.; Song, W. M. J. Org. Chem. 1989,54, 261. (6) Part 8 of the series Aqueous High-Temperature Chemistry of Carbo- and Heterocycles. Katritzky, A. R.; Murugan, R.; Siskin, M. Energy Fuels, in this issue.
The model compounds used in this study are anisole, diphenyl ether, n-butyl phenyl ether and 2,3-dihydrobenzofuran.
Experimental Section The gas chromatographic behavior of all the compounds encountered in this work (starting materials and products) is summarized in Table I. Table I1 records the source and mass spectral fragmentation patterns of the authentic compounds used, either BS starting materials or for the identification of products. Tables I11 and IV record the mass spectral fragmentation patterns of products for which authentic samples were not available and which were identified by comparison with literature MS data (Table 111) or by deduction (Table IV). The aquathermolyses were conducted as previously d e ~ c r i b e d and , ~ the results are collected in Tables V-VII. Tables I1 and I11 have been deposited as supplementary material (see paragraph a t end of paper regarding supplementary material).
Mass Spectral Assignments of Structures Arrival at the final structures for the compounds in Table IV was reached by considering the fragmentation (7) Part 1 of the series Aqueous High-Temperature Chemistry of Carbo- and Heterocycles. Katritzky, A. R.; Lapucha, A. R.; Murugan, R.; Luxem, F. J.; Siskin, M.; Brons, G. Energy Fuels, in this issue.
0~~~-062~/90/2504-0543$02.50/0 0 1990 American Chemical Society
