1494 SHABTAI, KLEMM, AND TAYLOR
The Journal of Organic Chemistry
Alumina-Catalyzed Reactions of Hydroxyarenes and Hydroaromatic Ketones. 111. Reactions of 2-Methyl-, 4-Methyl-, and 2,4-Dimethyl-l-naphthols with Methanol. Sequential Pathways to Polyrnethylnaphthalenesl* J. SHABTAI,'~ L. H. KLEMM, AND D. R. TAYLOR'~ Department of Chemistry, University of Oregon, Eugene, Oregon 97403 Received October 3, 1967 The alumina-catalyzed reactions of methanol with 1-naphthol (I), 2-methyl-1-naphthol (V), 4-methyl-1-naphtho1 (VI), and 2,4-dimethyl-l-naphthol (VIIa) were studied under comparable conditions a t 350-420'. Quantitative identity in the composition of methylnaphthalenes from I and V indicates that methylation of I at C-2 is a primary step with no major influence on the extent of subsequent substitution. The reactions of VI and VIIa are highly selective and give 1,2,4-trimethylnaphthaleneand 1,2,4,7-tetramethylnaphthaleneas main products (combined yields, 61-87 mol 70). A general, sequential pathway is proposed for formation of polymethylnaphthalenes from 1-naphthols. Data on the composition of the total methylnaphthalene product from I a t different reaction temperatures are used to estimate the relative over-all extents of ring methylation at C-2, C-4, and C-7.
As an extension of research on alumina-catalyzed On the other hand, the composition of methylnaphreactions of hydroxyarenes and hydroaromatic kethalene products formed from 4-methyl-1-naphthol (VI) or 2,4-dimethyl-l-naphthol (VIIa) differs markedly t o n e ~ , *a* ~comparative study was made of the reactions of methanol with 1-naphthol (I), 2-methyl- 1from that produced from I or V. (a) No 1,Pdimethylnaphthol (V), 4-methyl-1-naphthol (VI), and 2,4naphthalene is found, but the isomeric 1,3-dimethyldimethyl-1-naphthol (VIIa), respectively. The experinaphthalene is formed in small yield instead. (b) mental and analytical procedures were essentially the Only a single trimethylnaphthalene, i.e., the 1,2,4 same as described previously. Reactions were isomer (XVII), is produced. In fact, at 420" with the carried out at two selected temperatures, 350 and 420", weakly acidic catalyst C (expt 5 and 9) the reaction over catalyst A (pure alumina, obtained by hydrolysis can be conveniently employed as a preparative method of aluminum isopropoxide) and catalyst C (Houdry for XVII (60-66 mol %). ( c ) Yields of 1,2,4,7hard alumina, which contains ea. 0.4% of s o d i ~ m ) . ~ - ~tetramethylnaphthalene (XXI) are notably higher I n the temperature range studied A is distinctly more from VI or VIIa (40 mol yo at 420" with A, cf. expt acidic than C 2 g 3 6 and lo), while yields of the pentamethyl (XXII) and As seen from Table I the composition of methylhexamethyl (XXIII) compounds are slightly higher naphthalene products formed by the reaction of V with than those from I or V. Thus, the initial introduction methanol varies with reaction temperature and catalyst into I of a methyl group at C-4 fosters the forma,tion used. However, in :dl cases (expt 1-4) the di-, penta-, of 1,2,4-trimethyl- arid 1,2,4,7-tetramethylnaphthaland hexamethylnaphthalene fractions consist only of enes, while a t the same time it completely inhibits the one isomer each, viz. 1,2- (XIV), 1,2,3,4,6- (XXII), pathways to 1,Bdimethyl- and 1,2,7-triniethylnaphand (where present) 1,2,3,4,6,7- (XXIII), respectively. thalenes. The yield of XIV is higher with catalyst C than with A, I n Schemes I and I1 are depicted typical proposed while yields of XXII and XXIII are higher with the pathways for the formation of methylnaphthalenes more strongly acidic A. Three trimethylnaphthalenes, from reaction of methanol with 1-naphthol, as based 1,2,3- (XVI), 1,2,4- (XVII), and 1,2,7- (XVIII), and two tetramethylnaphthalenes, 1,2,3,4- (XIX) and SCHEME I 1,2,4,7- (XXI), are also formed. Among the former XVIII is the major component with A (expt 3 and 4), whereas XVII predominates with C (expt 1 and 2 ) . XXI is the major tetramethyl isomer with either catalyst. With A the composition of methylnaphthalene products from V is closely similar to that from I (cf. expt 3 and 11; 4 and 12). This result is consistent with previous observations that methylation of I produces V as the predominant isolable methylated naphthol under mild reaction conditions (275-350°)* and indicates that up to 420" methylation of I occurs more readily at C-2 than at any alternative ring position (vide infra:). CH3 293
(1) (a) This investigation was supported by Research Grants No. CA-5969 from the National Cancer Institute and No. GM 12730 from the National Institute of General Medical Sciences, U. 8 . Public Health Service. (b) On leave from the Department of Chemistry, Weismann Institute of Science, Rehovoth, Israel. (I:) Research Assistant, 1964-1967. (2) Part I: L. H. Klemm, J. Shabtai, and D. R. Taylor, J . Org. Chem., 88, 1480 (1968). (3) Part 11: J. Shabtai, I,. H. Klemm, and D. R. Taylor, ibid., 88, 1489
(1968).
(4) For simplicity, compounds and catalysts are designated by the same Roman numerals and capital letters, respectively, as used in part 1.2
VIIa
. , C y % p ;0 /
~
H3c$cH3 \
CH3
& = acidic site on the alumina surface
/
CH3 XXI
Vol. 33, No. 4, April 1968
HYDROXYARENES AND HYDROAROMATIC KETONES. I11 1495
TABLE I ALUMINA-CATALYZED REACTIONS OF 2-METHYL-1-NAPHTHOL AND 2,4-DIMETHYL-1-NAPHTHOL
Expt no. Starting naphthol Catalyst Reaction temp, 'C Conversion,c mol % Product component,d mol % ' 1,2-Dirnethyl-Ne (XIV) 1,3-Dimethyl-N 1,2,3-Trimethyl-N (XVI) 1,2,4-Trimethyl-N (XVII) 1,2,7-Trirnethyl-N (XVIII) 1,2,3,4-Tetramethyl-N (XIX) 1,2,4,7-Tetramethyl-h' (XXI) 1,2,3,4,6-Pentamethyl-N (XXII) 1,2,3,4,6,7-Hexameth>l-N (XXIII) Others Unidentifiedk
1
2
3
4
V
V
V
V
C 350 65
C 420 98
A 350 76
A 420 100
23.5
30.5
...
...
1.7 8.4 6.0 1.4 7.2 3.2
1.9 12.5 10.4 3.0 12.6 8.1 Trace 9.5 (9.0)
...
10.3 (3.5)
18.2
...
4.6 5.2 8.5 3.2 8.0 10.5 1.4 9.8 (4.8)
15.7
...
4.0 5.8 18.2 3.0 15.8 18.4 5.5 9.2f (3.0)
(v),4-METHYL-l-NAPHTHOL
(VI),
( V I h ) WITH htETHANOL" 5 VI C 420
100
6 VI
7 VIIa
A 420 100
C
VIIS A
8
350 86
350 95
,..
...
...
...
1.3
1.1
4.5
3.4
9 VIIa
10 VIIa
C
h
420 100
420 100
llb
I A 350 87 18.0
1.5
1.5
4.0 5.7 18.0 3.1 15.5 18.7 5.6 9.5i (3.5)
...
...
...
60.3
22.4
51.0
36.1
66.2
20.3
2.2
1.9 39.4 20.1 6.6 7.7' (0.5)
1.6 20.4 9.2 0.2
...
2.4 40.3 21.0 7.5 6.0h
4.5 5.3 8.2 3.6 7.9 10.2 1.3 22.oi
(0.5)
10.6)
(4.5)
20.1 8.6 0.i 1.0
(4.4)
...
. I .
2.5 12.3 3.6
...
...
(11.7)
... 2.9 29.2 10.8 1.6 1.5 (8.5)
15.5
...
...
.,.
I A 420 100
...
...
. . I
12b
A mixture of 0.012qimol of the naphthol and 20 g (0.63 mol) of methanol was used as starting material in each experiment. This Small changes from previous data2 in the composisolution was introduced into the reactor a t a uniform rate during a period of 2 hr. tion of products formed are ascribed to differences in the naphthol-catalyst and the naphthol-methanol ratios used. c Conversion of the naphthol. Calculated on the basis of 100 mol of starting naphthol (including unreacted material). Differences between conversion and total products formed represent losses due to unrecoverable deposits on the catalyst. e N is naphthalene. / Includes 3.8 mol % of heptamethylnaphthalene (XXIV) and 1.7 mol % of octnmethylnaphthalene (XXV), as based on gas chromatographic data I-Methylnaphthalene, 2.0; XXIV, 3.9; and XXV, 1.8 mol yo. * XXIV, 3.9; XXV, 2.1 mol %. only. Includes 10.6 mol % of V. I Includes XXIV, 3.8; XXV, 1.9 mol %. Percentage by weight of total product. I t includes unidentified chromatographic peaks and nondistillable residues. a
SCHEME I1 A CH#H
4
CH3
A -
r
4
CH3 0
CH3 CH3
