Aqueous organic chemistry

Aqueous

organic

chemistry

5. Diary1 ethers: diphenyl ether, 1 -phenoxynaphthalene and 9-phenoxyphenanthrene” Michael

Siskin,

Alan

R. Katritzkyt

and Marudai

Balasubramanianl

Corporate Research Science Laboratory, Exxon Research and Engineering Company, Route 22 East, Clinton Township, Annandale, NJ 08801-0998, USA IDepartment of Chemistry, University of Florida, Gainesville, FL 3261 l-2046, USA (Received 16 July 1992; revised 29 October 1992)

Diary1 ether model compounds, representative of thermally stable cross-links in coals, are cleaved under aquathermolysis conditions. 1-Phenoxynaphthalene and 9_phenoxyphenanthrene, although inert to thermolysis in cyclohexane, were reactive under all the aquathermolytic conditions studied. Phenol and I-naphthol were the major products from 1-phenoxynaphthalene. 9-Phenoxyphenanthrene was more reactive and similarly yielded phenol and 9-hydroxyphenanthrene. In a reducing atmosphere (15% formic acid or 15% sodium formate) the 1-naphthol and 9-hydroxyphenanthrene products undergo slow reductive dehydroxylation. Diphenyl ether was unaffected at 315°C under both thermolytic and aquathermolytic conditions, except in the presence of 15% aqueous sodium formate or 15% phosphoric acid where phenol was formed. These facile acid-catalysed ether cleavages of 1-phenoxynaphthalene and 9-phenoxyphenanthrene in water at 31X, were markedly decreased in the presence of calcium montmorillonite, CaCO,, LiCI, NaCl, KCl, KBr, MgSO,, BaSO,, Na*SO,, and inhibited by Na,CO,. The rate of reaction for cleavage of these diary1 ethers was inversely proportional to the concentration of the salts. (Keywords: water; diary1 ether; cleavage)

Coal can be considered to have a cross-linked macromolecular network structure of largely aromatic species connected by heteroatom and alkyl bridge structures2-14. The purpose of coal liquefaction processes’5-20 is to cleave the cross-links and obtain liquid products with increased hydrogen and reduced heteroatom content. Studies of the conversions of coal-related organic compounds under coal liquefaction conditions of >4OO”C have shown that polycyclic aromatic ethers undergo thermal radical cleavage reactions2,3. The carbon-oxygen bond in alkyl and alkyl aryl ethers is known to be a thermally weak link whereas diary1 ethers are essentially unreactive under liquefaction conditions”. Thermolyses of diary1 ethers have been studied at temperatures >4OO”C where the favoured radical pathways2*3 mask any contribution from ionic chemistry which could occur at lower temperatures in the presence of liquid water. Aqueous coal liquefaction offers several potential advantages over conventional liquefaction schemes, especially for low rank resources. The use of water as a medium in coal models, and in liquefaction processes, has been studied2’. These studies indicate that, under various conditions, water may act as a good liquefaction medium, dissolve or extract coal-derived liquid products, promote the cleavage of certain bonds likely to be found in components of coal, provide hydrogen through rhe *A preliminary

communication

of part of this work has appeared

Reference I 0016-2361/93/10/1435-10 r: 1993 Butterworth-Heinemann

Ltd.

in

water-gas shift reaction, and possibly assist the physical contact of the coal with catalysts or hydrogen. Previous studies in our laboratories showed that activated diary1 ethers are unreactive thermally at 350°C but aqueous chemistry provides ionic pathways for cleavage of these types of carbon-oxygen-carbon cross-links which are abundant in coals14. We now report that even the unactivated diary1 ethers, l-phenoxynaphthalene and 9-phenoxyphenanthrene, are susceptible to cleavage in water. The reactions are catalysed by water which is a stronger acid at high temperature (-log K, = 11.20 at 250°C and 11.30 at 300°C vs. 13.99 at 25”C)22. The cleavage reactions in liquid water and subsequent reduction reactions observed in the presence of formic acid and sodium formate are facilitated by the ability of the larger ring systems to undergo C-protonation, which parallels the ability of the corresponding hydroxy derivatives of the polycyciic ring systems to tautomerize to the keto-form. The importance of keto-enol tautomerism followed by rate-determining homolysis of the cyclohexadienone intermediate has been demonstrated in the thermolysis of a hydroxyphenyl phenyl ether at 400°C in tetralin”. There has been speculation concerning the potential ability of water to effect hydrolysis and cleavage of carbon-oxygen-carbon cross-links in coa123S24. Graff and Brandes25 found that steam pretreatment of an Illinois No. 6 bituminous coal between 320°C and 360°C dramatically improved the yield of liquids obtained on subsequent conversion or solvent extraction. The steam-modified coals also swelled more in water and

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1435

Aqueous

organic chemistry.

5. Diary1 ethers: M. Siskin et al.

contained twice as many hydroxyl groups as the raw coal, leading to the hypothesis that steam reacts with ether linkages in the coal, forming hydroxyl groups and thereby substantially hydrolyses an important covalent cross-link in the coal structure13. These conclusions are consistent with model compound studies on ether reactivity in hot water 14. In addition, Bienkowski et aLz6 reported that pretreatment of Wyodak subbituminous coal at 240°C followed by liquefaction at 400°C in the presence of steam increased conversion by 32%. Khan et a1.27 concluded that steam pretreatment at 320°C did not enhance volatile yields, but low rank coals showed increased liquid yields on rapid pyrolysis. Subcritical steam pretreatment of Zap lignite and Wyodak coal over broad temperature and time ranges gave sharp increases in tar yields at shorter pretreatment times. Subsequent liquefaction of the pretreated coals showed no benefit except on samples pretreated for very long (about 5 h) times”. Mochida et a1.29 reported an improvement in liquefaction yields in a pyrene solvent system associated with a boiling water pretreatment. Ross and Hirschon3’ reported improvement in product quality from donorsolvent liquefaction of a hydrothermally pretreated coal. Pollack and co-workers 31 found that pretreatment with water at 300°C for 30 min resulted in a small but consistent improvement (2 to 6%) in methylene chloride and heptane solubles on liquefaction of Illinois No. 6 and Rawhide coals. Tse and co-workers3’ found that aqueous pretreatment of a Zap lignite and Rawhide subbituminous coal resulted in increased hexane solubles and when the pretreatment was followed by co-processing with a Maya crude at 425”C, a 6 to 8% increase in hexane solubles was obtained. To study prototype reactions for coal liquefaction processes, the following model compounds were chosen as representing the coal structure: phenanthrene for aromatic hydrocarbons; 9-hydroxyphenanthrene for phenolic groups; and diphenyl ether, l-phenoxynaphthalene and 9-phenoxyphenanthrene for unactivated diary1 ether bridge structures. The thermolyses and aquathermolyses of these compounds were studied at 315”C, over 3 days in the following solvents: (i) C,H,,; (ii) H,O; (iii) 15% aqueous HCO,H; (iv) 15% aqueous HCO,Na; (v) 15% aqueous H,PO,; and (vi) 15% aqueous Na,HPO,. The present study also deals with the effects of the following inorganic additives on the aquathermolytic reactions of l-phenoxynaphthalene and 9-phenoxyphenanthrene: CaCO,, calcium montmorillonite, and a variety of salts: LiCl, NaCI, KCl, KBr, MgSO,, BaSO,, Na,SO, and Na2C03. EXPERIMENTAL 1-Phenoxynaphthalene and 9-phenoxyphenanthrene were prepared from the corresponding aryl bromides and phenol according to literature procedures33T34. The other compounds were obtained from commercial sources. All were found by gas chromatography to be of suitable purity (>99%) and were used without further purification. Calcium montmorillonite and the inorganic additives CaCO,, LiCl, NaCl, KCl, KBr, MgS04, BaSO,, Na2S04 and Na,CO, were all of reagent grade, and were obtained from commercial sources. The gas chromatographic behaviour of all the compounds encountered in this work (starting materials and

1436

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Table 1

No. 1 2 3 4 5 6 I 8 9

10 11

Structureandidentification

ofstarting

materials

and products

fR (min)

Structure’

Mol. wt

Response factor

1.80 3.52 3.70 6.11 6.50 8.00 9.75 10.70 12.40 14.25 17.75

Phenol 1,2-Dihydronaphthalene Naphthalene l-Tetralone Diphenyl ether I-Naphthol 9,10-Dihydrophenanthrene Phenanthrene I-Phenoxynaphthalene 9-Hydroxyphenanthrene 9-Phenoxyphenanthrene

94 130 128 146 170 144 180 178 220 194 270

0.79 0.95 0.95 0.77 0.74 0.77 0.93 0.93 0.72 0.75 0.70

“In every instance the structure

was identified by reference to Table 2

products) is summarized in Table I. Table 2 records the sources and mass spectral fragmentation patterns of the authentic compounds used, either as starting materials or for the identification of products. The aquathermolytic reactions and analyses of products were conducted as previously described35 and the results are collected in Table 3 to Table 9. In all aqueous experiments a liquid water phase was maintained (7 ml of solution and 1.0 g of compound in an 11 ml T316SS reactor). Pressures ranged from about 1054 605 kg m-* (1500 psi) in water to about 2 320 131 kg me2 (3300 psi) in formic acid. All conversions are in moles as a per cent of the starting material. RESULTS AND DISCUSSION In the reaction schemes numbers greater than, or equal to, 100 are used for intermediates not detected by the g.c.-m.s. system. Diphenyl ether, 1-phenoxynaphthalene, phenanthrene, 9-hydroxyphenanthrene and 9-phenoxyphenanthrene did not undergo thermolysis in cyclohexane at 315°C over 3 days. l-Phenoxynaphthalene and 9-phenoxyphenanthrene failed to react even in the presence of CaCO, or calcium montmorillonite. Diphenyl ether (5)

Aquathermolysis of diphenyl ether at 315”C, over 3 days, showed no reaction (Table 3 and Scheme 1). It was also unaffected in 15% formic acid. However, with 15% sodium formate diphenyl ether underwent hydrolysis to phenol 6.6%. Acid catalysed hydrolysis occurred in 15% aqueous phosphoric acid to give 92.3% conversion to phenol. It is reasonable that both base (sodium formate) and acid catalysed hydrolyses occur*. Acidic hydrolysis was achieved with the strong phosphoric acid, but formic acid was too weak to give detectable amounts of phenols. Nucleophilic attack on the ortho-protonated diphenyl ether molecule (100) or direct attack of hydroxide on diphenyl ether results in the formation of intermediates which collapse to phenol, etc. *Independent n.m.r. observation made by Dr G. P. Miller indicated diphenyl ether is deuterated at least two orders of magnitude faster at the ortho than the para position in D,O at 315°C. Similarly, I-phenoxynaphthalene is deuterated faster at the 2-position of the naphthalene ring than at the two ortho-positions of the phenyl ring, deuteration at these positions being at least an order of magnitude faster than at any other position

Aqueous Table 2

Properties

of authentic

compounds

used as starting

organic chemistry. 5. Diary1 ethers: M. Siskin et al.

materials and for the identification of products ~~~. _ .~___ Fragmentation pattern m/z (% relative intensity, structure of fragmentation)

Original No. 1

Mol. wt

Compound Phenol

Purity

94

F

100.0

94(100); 66(50); 65(40); 40(15)

100.0

130(100);

129(80);

100.0

128(100);

127(10); 102(5); 75(10); 63(10)

3886” 6791b

2

1.2-Dihydronaphthalene

130

A

3

Naphthalene

I28

A

4

1-Tetralone

5

Diphenyl

ether

Ref

Source”

893’

128(95); 115(85);

146

F

100.0

170

A

100.0

170(100);

142(25);

770’

141(40); 77(60): 51(50)

6

1-Naphthol

144

F

99.9

144(100);

116(40); 115(70); 63(15): 39(5)

1

9,10-Dihydrophenanthrene

180

A

99.9

180(100);

179(65); 178(30);

8

Phenanthrene

178

A

100.0

9

I-Phenoxynaphthalene

220

P

100.0

10

9-Hydroxyphenanthrene

194

A

100.0

194(100);

165(50); 115(10); 82(20): 63(5)

11

9-Phenoxyphenanthrene _.__

270

P

100.0

270(100);

269(20); 241(20);

Mass Spectral

274’

104(20)

146(65); 118(100); 90(95); 89(50): 63(45)

“A= Aldrich, F = Fischer, P = prepared *The mass spectral data given here are from a search of the EPA/NIH Standards, 1978 to 1980 ‘The numbers are page . - numbers from the books mentioned in footnote “Wilson, J. M. Erperientia, 1960, 16, 403

(MS)

402’

165(20); 89(5)

13175b

178(100);

176(15); 152(10); 89(15); 76(10)

220(100);

219(50);

12779b d

Data

191(40); 115(60): 77(30)

15416b d

165(50); 77(15)

Base: S. R. Heller. G. W. Milne:

National

Bureau

of

b

1 Nu-

1

Scheme 1

I-Phenoxynaphthalene (9) Aquathermolysis of 1-phenoxynaphthalene at 315°C for 24 h gave phenol (1) (84.6 mol%) and 1-naphthol (6) (84.2 mol%) together with a trace of naphthalene (3) (0.4 mol%) (Table 4 and Scheme 2). After 3 days, 9 showed conversion to phenol (94.6 mol%), naphthol (92.4 mol%), naphthalene (0.4 mol%), and in addition 1-tetralone (4) (1.8 mol%) which presumably formed by reduction of small amounts of the 1-naphthol. I-Phenoxynaphthalene with 15% formic acid and with 15% sodium formate Formic acid and sodium formate are known to be strong reducing agents36. Under aquathermolytic

Table 3 Products for 3 days No.

Solvent

1 5

Phenol Diphenyl

of aquathermolysis

ether

of diphenyl

ether (5) at 3 15 ‘C

15% HCO,Na

15% H,PO,

6.6 93.4

92.3 7.7

conditions they release hydrogen which is the source for partial hydrogenation of the aromatic hydrocarbons. However, 15% formic acid, although it completely converted 1-phenoxynaphthalene over 72 h, gave phenol (100 mol%) and 1-naphthol (6) (98.6 mol%), with only traces of naphthalene (0.8 mol%) and 1-tetralone (0.6

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Aqueous Table 4

organic chemistry.

5. Diary1 ethers: M. Siskin et al.

Products of aquathermolysis of 1-phenoxynaphthalene

Solvent

15% HC02H

Hz0

Time (h)

2

No.

Structure

1

Phenol

2

1,2-Dihydronaphthalene

3

Naphthalene

4

l-Tetralone

6

l-Naphthol

9

l-Phenoxynaphthalene

4.5 _

15% Na,HPO,

72

12

2

0.5

72

84.6 _

94.6 _

36.6 _

91.6 _

41.4 _

0.4

24.6 5.8 5.8

46.5 _

0.4

100 _ 0.8

-

_

13.0

46.5

90.4

39.3

15.4

53.5

8.4

58.6

_

1.8

0.2

0.6

-

4.5

84.2

92.4

36.4

95.5

15.4

5.4

63.4

98.6 -

I-Phenoxynaphthalene with 15% phosphoric acid and with 15% disodium hydrogen phosphate

Ar-0 bond cleavage was strongly catalysed by 15% phosphoric acid. Heating at 315°C for 30 min, 1-phenoxynaphthalene showed 91.6% conversion to its hydrolysis products with traces of naphthalene (0.8 mol%) and 1-tetralone (0.4 mol%), see Table 4. With 15% aqueous Na,HPO,, during 3 days, it underwent only 41.4% conversion and again the products were mainly phenol (41.4 mol%) and I-naphthol (39.3 mol%) although a significant amount of reduction to naphthalene (2.1 mol%) was observed. with CaC03 and calcium

The reactivity of 1-phenoxynaphthalene (9) to aquathermolysis (Table 5) was completely inhibited at 3 15°C (3 days) in the presence of basic CaCO, (1 mol equivalent). In the presence of acidic calcium montmorillonite hydrolysis gave phenol (64.2 mol%), and 1-naphthol (6) (63.4 mol%) along with a trace of naphthalene (3). Calcium montmorillonite is an acidic clay mainly composed of Al,O, and SiO,, but surprisingly the reaction rate is lower than in water alone. with aqueous NaCI, KCI, LiCI

In order to better understand the effect of brine in cross-link cleavage reactions, the 1-phenoxynaphthalene (9) was heated at 315°C over 3 days with various concentrations of aqueous NaCl (Table 5). With O.l%, 0.5% and 1% NaCl, the ether showed 46%, 29% and 7.4% conversions and the main products were phenol and naphthol. On aquathermolysis at 315°C over 2 h, 9 showed no reaction in 1% NaCl alone. This is counter to what was previously observed with cyclohexyl phenyl ether37. In the presence of 1% H,PO, and 1% NaCl,

1438

15% H,PO,

2

mol%) (as an oxidation product of naphthol), see Table of the 2 h run in formic acid (36.6% conversion) with the 2 h run in water (4.5% conversion) clearly shows that acid catalysed hydrolysis, rather than the reduction properties of formic acid, were important. At 315X, with 15% sodium formate over 3 days, 1-phenoxynaphthalene underwent 24.6% conversion to give the following products: phenol (24.6 mol%), 1,2_dihydronaphthalene (2) (5.8 mol%), naphthalene (3) (5.8 mol%) and 1-naphthol (6) (13.0 mol%): thus, reaction was slower than in acid or water, but reduction was of greater importance.

I-Phenoxynaphthalene and KBr

1% H,PO,

72

4. Comparison

1-Phenoxynaphthalene montmorillonite

15% HCO,Na

24

0.4 _

(9) at 315°C (mol%)

Fuel 1993 Volume 72 Number 10

_

0.8 0.4

2.1 _

15.8% conversion to phenol and naphthol was obtained in 2 h. Clearly the rate of acid catalysed hydrolysis is suppressed by the presence of the salt (cf. Table 4). The ether showed no reaction in 5% or 15% NaCl and also no reaction in the presence of CaCO, or BaSO,. In 15% aqueous NaCl in the presence of the acidic clay, calcium montmorillonite (1 mol equivalent), conversion was 19.4% over 3 days and the same three products (phenol, naphthalene and 1-naphthol) were identified. Only 6.7% conversion over 3 days was obtained when 1 mol equivalent of MgSO, (see below) was added to the 15% NaCl solution. Similar inhibitions were observed when the aquathermolyses were run at 315°C in the presence of 1% KC1 (only 8.1% conversion in 3 days), 1% LiCl (4.8% conversion in 3 days) or 1% KBr (3.8% conversion in 3 days). In each case the same two phenols were obtained, usually accompanied by a trace of naphthalene. These results indicate no significant effect of cation activity on the ether cleavage reaction. I-Phenoxynaphthalene

with MgSOI, BaS04 and Na2S04

Aquathermolysis of 1-phenoxynaphthalene (9) with the acidic salts 1% MgS04 or 1% BaSO, over 3 days at 315°C showed 52.5% and 30.5% conversion, respectively, to give equimolar amounts of phenol and 1-naphthol (Table 5). However, with neutral 1% Na$O,, 9 showed no reaction. These acidic salts also clearly reduced the rate of ether cleavage, but not as dramatically as NaCI, KCl, LiCl and KBr which was generally assumed to be devoid in acidic or basic character. Complete inhibition of the hydrolysis of 1-phenoxynaphthalene over 3 days at 315°C was also caused by aqueous 1% pyridine or 1% Na,CO,. These findings support the evidence for a dominant acid catalysed mechanism for this reaction. The base catalysed hydrolysis must be too slow to give detectable products under conditions used. Mechanistically, hot water acts as an acid to protonate 1-phenoxynaphthalene. Nucleophilic attack of water on a protonated 1-phenoxynaphthalene (103) leads to intermediate 104, which loses phenol to give 1-naphthol (6). Intermediates 105 and 108 are tautomeric forms of I-naphthol (6), and they undergo reduction to furnish 1,2-dihydronaphthol (106) and 3,4-dihydronaphthol (109), respectively. Formic acid and sodium formate are the hydride ion sources for the reduction processes as shown. Intermediate 107 either loses water to give naphthalene (3) or is further reduced to yield 1,2_dihydronaphthalene (2).

Aqueous

organic chemistry.

5. Diary/ ethers: M. Siskin et al.

- PhOH

+ JO* t

6

i-l 1 &k

108

k

0

OH

106

4

107 - H20 I

2

Scheme 2

We have already reported that salts such as NaCl and Na,SO, undergo hydrolysis at high temperatures in aqueous solution, and pointed out that this is reflected in the volatility of mineral acids at high temperatures from solutions of salts such as sodium chloride*‘. Even sulfuric acid is volatile in hydrothermal media so sulfates

would also somewhat increase the basicity of such solutions38. The hydrolysis of Smethoxynaphthalene was shown to be enhanced by small quantities (up to 1%) of added NaCl, but the work was done in supercritical water (390°C) where radical type reactions become important at densities below the critical point39.

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1439

Naphthalene

I-Naphthol

1-Phenoxynaphthalene

3

6

9

54.0

44.6

1.4

46.0

72

-

Structure

9,10-Dihydrophenanthrene

Phenanthrene 9-Hydroxyphenanthrene

No.

1

8 10

9-Phenoxyphenanthrene

11

92.7

2.1

2.5

Phenanthrene

9-Hydroxyphenanthrene

2.1

1.3

Phenol

9,10-Dihydrophenanthrene

1

I

24

Hz0

4.3

93.0

20.0

1.8

0.9

7.0

24

71.5

4.5

4.0

80.0

72

76.0

20.3

2.5

1.2

24.0

72

0.1% NaCl

95.5

2.3

1.2

1.0

4.5

24

87.9

8.3

2.1

1.1

12.1

72

0.5% NaCl

(11) at 250°C (mol%)

2.2 97.8

_

12

Time (h)

Structure

8

84.2

15.8

-

15.8

2

1% H,PO,

92.6

96.5

1.2

1.7

1.0

3.5

6.9 89.1

2.6

1.4

10.9

72

1% NaCl 24

5.8

1.6

7.4

72

-

1.8 2.8 5.9 89.5

0.8 1.8 1.3 96.1

10.5

72

1% LiCl

3.9

6.1

6.1

93.3

-

12

15% HCO,H

80.6

17.5

1.9

19.4

72

63.4 36.6

_

72

98.3

1.4

0.3

1.7

24

-

96.5

1.2

1.1 1.7

89.8

5.4

1.9 2.9

10.2

72

4.8

4.8

96.1

1.0

0.6 1.3

96.2

3.6

0.2

3.8

12

_

1% KBr

92.1

4.3

0.8 2.8

1.9

72

98.5 _

21.1 74.0

95.0

1.5 3.4

26.0

72

2.2

0.2 2.6

5.0

24

41.5

52.5

52.5 -

96.8

1.2

0.6 1.4

3.2

24

16.9 78.6

1.3 3.2

21.4

72

1% BaSO,

1.8

7.8

92.2

_

72

_

1% MgSO,

24

_

1.5

12

1% MgSO,

15% HCO,Na

95.2

-

12

1% KBr

2.9

24

1% LiCl _

58.6 41.4

_

3

91.9

6.4

1.7

8.1

72

_

1% KC1

1% KC1

4.0

24

MgSO,

15% NaCl Mont*

24

4.4 95.6

_

2

(10) at 315°C

1.2 98.4

0.4

1.6

24

-

1% NaCl

of 9-hydroxyphenanthrene

71.0

28.1

0.9

29.0

72

_

Hz0

Products of aquathermolysis of 9-phenoxyphenanthrene

10

88.7

11.3

-

11.3

24

_

0.5% NaCl

Products of aquathermolysis

85.1

14.8

0.1

14.9

24

-

0.1% NaCl

(9) at 315°C (mol%)

Solvent

Table 6

35.8

63.4

0.8

64.2

No.

Time (h)

Solvent

Table 7

“1 mol equivalent bCalcium montmorillonite

Product

Phenol

72

Time (h)

1

Month

Additive”

No.

Hz0

Products of aquathermolysis of 1-phenoxynaphthalene

Solvent

Table 5

6.3

6.3

69.5

30.5

30.5 _

72

_

2.2

1.3

3.5

96.5

-

72

1% Na,SO,

93.7

_

24

_

1% BaSO,

Aqueous It seems probable that the enhancement of ionic type hydrolytic mechanisms by the NaCl is due to the increase in ionic strength as suggested39. We considered the salting-out effect as another possible explanation for the rate reductions in the presence of salts. We have rejected this because there is a dramatic and progressive reduction in the conversion of I-phenoxynaphthalene at O.l%, 0.5% and 1% concentrations of NaCl (Table 5). Salting-out effects are unlikely to be significant at concentrations down to these levels. Phenanthrene (8) In 15% aqueous formic acid, or 15% aqueous sodium formate, at 315”C, over 3 days, phenanthrene (8) underwent reduction to give small amounts of 9,10-dihydrophenanthrene (7) (0.5% and l%, respectively). This is analogous to previous work on coal-related aromatic model compounds carried out in the presence of carbon monoxide and water41-43.

organic chemistry.

5. Diary1 ethers: M. Siskin et al.

9-Phenox~~henanthrene and I % NaTSO,

,tlith 1 o/o MQSO~. I % BaS04

In the presence of 1% MgSO,, 1% BaSO, or 1% Na,SO, (Table 7) the aquathermolytic reactions of 9-phenoxyphenanthrene were also inhibited and showed only 26%, 21.4% and 3.5% conversion, respectively, at 25O’C over 3 days. Aquathermolysis of 9-phenoxyphenanthrene (II) at 315°C 9-Phenoxyphenanthrene (Table 8, Scheme 3) showed high reactivity at 3 15’C under aquathermolysis conditions. Over 1 h, 11 yielded phenol (1) (92.6 mol%), phenanthrene (8) (1.2 mol%) and 9-hydroxyphenanthrene (10) (91.4 mol%). After 3 h, conversion was essentially quantitative with some of the 9-hydroxyphenanthrene dehydroxylated to phenanthrene (19.4 mol%) which was further reduced to 9,10-dihydrophenanthrene (0.8 mol%) after 3 days. 9-Pheno.~~phenunthrene bvith,formic acid and sodium

FHydroxyphenanthrene

(10)

Aquathermolysis of 9-hydroxyphenanthrene (10) at 3 15”C, over 3 days (Table 6), yielded a small amount of phenanthrene (8) (2.2%). With 15% formic acid over 3 days, 10 was 63.4% converted into phenanthrene. 9-Hydroxyphenanthrene showed 100% conversion in 15% sodium formate over 3 days and the main product was again phenanthrene (98.5 mol%); the remainder was 9,10-dihydrophenanthrene (7) (1.5 mol%). From runs at the same temperature over 2 or 3 h, it is clear that the sodium formate is a more effective reducing agent than formic acid. The mechanism of these reductions exactly parallels those shown in Scheme 2 for 1-hydroxynaphthalene. Aquatllc~rzol~sis qf Y-phenoxyphenanthrene (11) at 250°C On heating in water at 25O”C, over 24 or 72 h, the larger 9-phenoxyphenanthrene ring system (Table 7, Scheme 3) was much more reactive and showed 7.3% and 80% conversions, respectively, the main products being phenol and 9-hydroxyphenanthrene (10). Small amounts of phenanthrene (6) and 9,10-dihydrophenanthrene (7) were also formed. Clearly there is some autocatalysis because the increasing concentrations of phenols cause a reduction in the pH of the solution. 9-Phewuyphrnanthrene KBr

(II) Ivith LiCI, NaCl, KC1 and

Our experiments indicate (Table 7) that the rate of hydrolysis of Ar--0 ether bonds in 9-phenoxyphenanthrene is inversely proportional to the concentration of NaCl, i.e. 24% and 10.9% conversion in the 72 h at 250°C runs for 0.1% and 1% NaCl, respectively. 9-Phenoxyphenanthrene showed the same trend as 1-phenoxynaphthalene towards 1% LiCl, 1% NaCl, 1% KC1 and 1% KBr. After heating for 3 days at 250°C with each of these aqueous salts, 11 showed 10.5%, 12.1%, 10.2%, 7.9% conversions, respectively. The products obtained in all cases were phenol, 9,10-dihydrophenanthrene (7), phenanthrene (8) and 9-hydroxyphenanthrene (10). Thus, these acid catalysed ether cleavage reactions of 9-phenoxyphenanthrene were strongly inhibited even by low concentrations of dissolved alkali metal halides.

formute

In 15% formic acid (Tab/e 8), 9-phenoxyphenanthrene readily underwent cleavage, showing complete conversion within 3 h at 315°C to give phenol, 9-hydroxyphenanthrene and phenanthrene. Heating at 315”C, for 3 days converted 11 into phenol (100 mol%), 9,10-dihydrophenanthrene (7) (0.8 mol%), phenanthrene (8) (51.6 mol%) and 9-hydroxyphenanthrene (11) (47.6 mol%). On heating with 15% sodium formate for 3 days at 3 15”C, 9-phenoxyphenanthrene gave phenol (47.6 mol%) and phenanthrene (47.6 mol%), as the only products. 9-Phenoxyphenanthrene montmorillonite

with CaCOj and calcium

Reactivity was reduced at 315°C in the presence of CaCO, (Table 9), where the main products were again phenol (47.8 mol%) and 9-hydroxyphenanthrene (10) (46.4 mol%). With calcium montmorillonite, reaction was complete in 3 days to produce phenol (100 mol%) and 9-hydroxyphenanthrene (100 mol%). 9-Phenosyphenanthrene

with 15% NaCl

Dramatically, 9-phenoxyphenanthrene (11) was unchanged (Table 9) during 3 days at 315”C, in 15% aqueous sodium chloride. At this concentration a salting-out effect might be expected. The introduction of 1 mol equivalent of each of the following additives to the system allowed cleavage to occur with the conversion factors noted: calcium carbonate (3.5 mol%), calcium montmorillonite (13.5 mol%), barium sulfate (28.8%) and magnesium sulfate (100%). The main products were phenol and 9_hydroxyphenanthrene, but some conversion of the latter to phenanthrene was also observed. 9-Phenoxyphenanthrene did not show any reaction in the basic systems containing 1% pyridine or 1% Na,CO, over 72 h at 315°C. Nucleophilic attack of water or formate on the protonated 9-phenoxyphenanthrene molecule (114) provides the intermediates 115 to 117. Loss of phenol from the intermediates 115and 116 furnishes 9-hydroxyphenanthrene (10) and phenanthrene (8), respectively. Intermediate 117 on hydrolysis, loses phenol to provide 9-hydroxyphenanthrene (10). Product 10 then undergoes further reduction to give 9,10-dihydrophenanthrene (7).

Fuel 1993

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Aqueous

organic chemistry.

/ d

5. Diary1 ethers: M. Siskin et al.

/ \

\ I /

I *NPh

11

0

- PhOH

H

7

Scheme 3

1442

Fuel 1993 Volume 72 Number 10

H

110

Aqueous Table 8

Products

of aquathermolysis

of 9-phenoxyphenanthrene

Solvent

No.

(11) at 315°C (mol%)

H,Q

Time (h)

15% HCO,H ~-~~~

-~

1

3

12

1

92.6

97.0

99.6

83.0

15% HCO,Na

3

12

12

100

100

Structure

1

Phenol

I

9,10-Dihydrophenanthrene

0.8

_

8 IO

Phenanthrene 9-Hydroxyphenanthrene

1.2 91.4

4.5 92.5

19.4 19.2

6.5 76.5

11

9-Phenoxyphenanthrene

7.4

3.0

0.4

17.0

Table 9

5. Diary1 ethers: M. Siskin et al.

organic chemistry.

Products

of aquathermolysis

of 9-phenoxyphenanthrene

47.6

0.8 13.0 87.0

51.6 47.6

47.6 _

-

52.4

(11) at 315°C (mol%)

Solvent

15% NaCl

H,Q

Additive”

CaCO,

Month

Mont*

CaCO,

Month

BaSO,

MgSQ,

Time (h)

72

1

72

72

72

12

72

100

No.

Structure

I

Phenol

8

Phenanthrene

47.8 1.4

1.3 _

10

9-Hydroxyphenanthrene

46.4

1.3

11

9-Phenoxyphenanthrene

52.2

98.7

100

3.5

13.5

28.8

_

0.5

2.5

3.4

18.4

100

3.0

11.0

25 4

81.6

96.5

86.5

71 2

“1 mol equivalent bCaIcium montmorillonite

CONCLUSIONS Three unactivated diary1 ethers, diphenyl ether, lphenoxynaphthalene and 9_phenoxyphenanthrene, have been heated under aqueous conditions at 250°C and at 3 15°C over 3 days. While diphenyl ether was stable except in the presence of 15% sodium formate and 15% phosphoric acid, 1-phenoxynaphthalene and 9-phenoxyphenanthrene both showed high cleavage reactivity. Generally, the rate of cleavage of the diary1 ethers increased with increasing number of rings in the structure. The rate of conversion of phenyl aryl ethers increased in the following order with respect to the aryl group: phenyl < 1-naphthyl < 9-phenanthryl and is facilitated by the ability of the larger aromatic ring systems to undergo C-protonation. Dehydroxylation of the cleavage products 1-naphthol and 9-phenanthrol was observed under reducing conditions, e.g. HCO,H or NaOOCH. The aquathermolyses at 315°C show that water can act as a proton donor leading to hydrolysis of multi-ring diary1 ethers. Structures of this type are major covalent cross-links in the macromolecular structure of coals which are not readily cleaved thermally, but could be broken down via ionic pathways by water or aqueous acid at high temperatures to produce higher yields of liquids. Studies of the aquathermolytic reactions of lphenoxynaphthalene and 9-phenoxyphenanthrene with solid CaCO,, calcium montmorillonite or dissolved LiCl, NaCl, KCl, KBr, MgSO,, BaSO,, Na,SO, and Na,CO, showed that these salts suppressed the hydrolytic cleavage of Ar0 linkages. The reactions were strongly inhibited by the presence of basic CaCO, and in NaCl, KCl, LiCl and KBr, but only slightly inhibited by acidic calcium montmorillonite and MgSO, and neutral Na,SO,. These acid catalysed Ar0 ether cleavage

reactions were completely inhibited in the more strongly basic 1% Na,CO, and by 1% pyridine. We have postulated4’ that at these high temperatures alkali halides behave as salts of strong bases and weak acids in water. REFERENCES 1

8 9 10 11 12 13 14 15 16 17 18 19 20

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McMillen, D. F., Malhotra, R., Chang, S. J., Ogier, W. C., Nieenda. S. E. and Fleming. R. H. Fuel 1987, 66, 1611 Marshali, W. L. and Fran& E. U. 3. Phys. Chem. Ref. Data 1981, 10, 295 Chung, K. E., Goldberg, I. B. and Ratto, J. J. ‘Rockwell International Interim Report No. AP-3889’, EPRI, Palo Alto, February 1985 Ross, D. S. in ‘Coal Science’ (Eds M. Gorbaty, J. Larsen and I. Wender), Academic Press, New York, 1984, Vol. 3 Graff, R. A. and Brandes, S. D. Energy Fuels 1987, 1, 84 Bienkowski, P. R., Narayan, R., Greenkorn, R. A. and Chao, K. C. Ind. Eng. Chem. Res. 1987,26, 202 Khan, M. R., Chen, W.-Y. and Suuberg, E. Energy Fuels 1989, 3, 223 Serio, M. A., Solomon, P. R., Kroo, E. and Charpenay, S. Prepr. Am. Chem. Sot. Div. Fuel Chem. 1991, 36, I Mochida, I., Moriguchi, Y., Iwamoto, K., Fujitsu, H., Korai, Y. and Takeshita, K. ‘Proceedings of the Japan/US NSF Chemistry of Coal Liquefaction Meeting’, 1985, p. 25 Ross. D. S. and Hirschon. A. S. Prevr. Am. Chem. Sot. Div. Fuel’Chem.

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Tse, D. S., Hirschon, A. S., Malhotra, R., McMillen, D. F. and Ross, D. S. Prepr. Am. Chem. Sot. Div. Fuel Chem. 1991, 36, 23 Bacon, R. G. R. and Stewart, 0. J. J. Chem. Sot. 1965,4953 Huang, R. L. J. Chem. Sot. 1955, 3295 Katritzky, A. R., Lapucha, A. R., Murugan, R., Luxem, F. J., Siskin, M. and Brons, G. Energy Fuels 1990, 4, 493 Gibson, H. W. Chem. Rev. 1969, 69, 673 Siskin, M., Brons, G., Katritzky, A. R. and Murugan, R. Energy Fuels 1990, 4, 482 Cobble, J. W. and Lin, S. W. in ‘ASME Handbook on Water Technology for Thermal Power Systems’ (Ed. P. Cohen), ASME, 1989 Penninger, J. M. L. and Kolmschate, J. M. M. in ‘Supercritical Fluid Science and Technology’ (Eds K. P. Johnston and J. M. L. Penninger), ACS Symposium Series No. 406, ACS, Washington, DC, 1989, pp. 242-258 Katritzky, A. R., Balasubramanian, M. and Siskin, M. Chem. Commun. 1992, 1233 HorvBth, I. T. and Siskin, M. Energy Fuels 1991, 5, 932 Stenbera. V. I.. Wane. J.. Baltisbereer. R. J.. Van Buren. R. and Wools& N. c. J. 0;s. Chem. 197{, 43, 2941 Baltisberger, R. J., Stenberg, V. I., Wang, J. and Woolsey, N. F. Prepr. Pap. ACS Div. Fuel Chem. 1979, 24, 14