ORIENTATION IN THE FRIES REARRANGEMENT OF PHENYL

[COXTRIBUTION FROM

TEE

RESEARCHLABORATORY OF ARMOURAND COMPANY ]

ORIEKTATION I?: T H E FRIES REARRANGEMENT O F PHEh'YL CAPRYLATE A. W. RALSTON, M. R. McCORKLE,

AND

E. W. SEGEBRECHT

Received April 81, 1941

Any explanation of the mechanism of the Fries rearrangement should be based upon the fact that metallic complexes and not the original components are the reacting substances. Some of these complexes have been isolated and identified while others still have a hypothetical existence. Phenoxyaluminum dichloride was shown to be a reacting component by Sandulesco and Girard (1) and the formation of an acid chloride-aluminum chloride complex was demonstrated by Perrier (2), Boeseken (3) and Kohler (4). A ketone-aluminum chloride complex was isolated by Olivier ( 5 ) , and it was stated by this author and also by Groggins (6) that this complex could not promote further acylations. Recently Ralston, McCorkle, and Bauer (7) have shown t h a t the products resulting from a Fries rearrangement are dependent upon the molecular ratio of aluminum chloride employed and have suggested that there is a relation between the amount of aluminum chloride and the reacting complexes present. Previous knowledge of the Fries mechanism has been obtained from the completed reactions rather than a study of the reaction a t intermediate points. Some knowledge of the mechanism of the rearrangement should be obtained by a study of the reaction products present a t intermediate points. We have, therefore, made a study of the rearrangement of phenyl caprylate with the purpose of determining the products which are present a t a number of intermediate stages in the reaction. One series of runs has been made in which the amount of aluminum chloride used was approximately molecularly equivalent to the ester, another series in which decidedly less aluminum chloride was used, and another in which the amount of aluminum chloride was materially in excess of an equal molecular ratio. In attempting to correlate these data we have also studied the rearrangement of phenyl caprylate by various aluminum chloride complexes rather than aluminum chloride itself. Table I shows the products obtained a t various time intervals when phenyl caprylate is rearranged in the presence of a 1.1 mole ratio of aluminum chloride in tetrachloroethane at 100". The increase in the value for p / o as the reaction progresses is extremely 750

751

THE FRIES REARRANGEMENT

significant. It can readily be seen that any comparison of the effect of reaction conditions upon orientation when equal molecular proportions of ester and aluminum chloride are used must take into consideration the percentage of ester rearranged. Another run under similar conditions using equal molecular proportions of ester and aluminum chloride gave, after fifteen minutes, 64% phenyl caprylate, 5.4% p-hydroxycaprylophenone, and 23.6y0o-hydroxycaprylophenone or a p / o value of 0.23. After six hours the ester decreased to 7.3% and the para and ortho hydroxy ketones increased to 29.1% and 58.5% respectively giving a value of 0.50 for p / o . In our previous work (7) upon the rearrangement of phenyl caprylate by aluminum chloride and also upon the acylation of phenol by caprylyl chloride, we have shown that an increase in the amount of aluminum chloride employed increased the value for the ratio p/o. It was shown that when there was only sufficient aluminum chloride present to form the TABLE I REARRANGEMENT O F P H E N Y L CAPRYLATE BY 1.1 MOLESOF ALUMINUM CHLORIDE AT 100". SOLVENT: TETRACHLOROETHANE % PARA

2 3 4 5

60 120

8.6 18.5 30.8 35.5 40.5

%ORTHO

18.2 29.5 32.2 41.0 43.1

1

%

EETER

66.0 46.5 30.8 18.2 10.5

PI0

0.47 .63 .95 .87 .94

complex CeH50A1C12a preferential ortho orientation was obtained, but if the complex C,HI6COC1.AlC1, is present the orientation is preferentially para. If the mechanism of the rearrangement of phenyl caprylate is a splitting followed by an acylation and removal of the aluminum chloride as a ketone complex, the ratio of aluminum chloride to reacting products should be highest at the initial stages of the reaction, and the orientation should be preferentially para during this period. Since this is not the case, it appears that the aluminum chloride must be rather firmly held by the ester. The addition of one-tenth mole of aluminum chloride to onetenth mole of phenyl caprylate dissolved in 50 cc. of tetrachloroethane produced a temperature rise of 20.5'. Since no hydrogen chloride was evolved and since an addition of the same amount of aluminum chloride to 50 cc. of tetrachloroethane produced no temperature rise, it appears that the ester itself forms a complex with aluminum chloride. This esteraluminum chloride complex is probably also present in the Friedel-Crafts

752

RALSTON, MCCORKLE, AND SEQEBRECHT

acylation of phenol, since partially completed reactions show substantial amounts of ester. The mechanism of the rearrangement as postulated by Rosenmund and Schnurr (8), Skraup and Poller (9), and also Cox (10) assumes that the ester splits into phenoxyaluminum dichloride and acid chloride, followed by a reaction of acylation. The rearrangement of the phenyl caprylatealuminum chloride complex would be as follows: CBH~OCC~HIS -+ CaH6OAlC12

II 0 I

+ C,H&OCl+

+

C ~ ~ A ~ O C B H ~ C O CHC1 ~HIS

AlCL In the acylation of phenoxyaluminum dichloride by caprylyl chloride, it has been shown that the acyl group replaces an ortho hydrogen preferentially, and it appears that ortho substitution predominates at the initial stage of the reaction. If this is the only reaction which takes place, however, it is difficult to explain why the value for p l o changes as the reaction proceeds. Since A1C120CsH&C7H1s contains the group A1Cl20-, previ-

II

0 ously shown to be reactive, and also the keto group, which could possibly remove aluminum chloride from the ester complex, it is probable that this product becomes a reacting component. In order better to evaluate the action of the various reacting complexes a series of runs was made in which materially less than a molecular equivalent of aluminum chloride was present. Table I1 shows the products obtained when phenyl caprylate is rearranged with 0.5 mole ratio of aluminum chloride in tetrachloroethane a t 100". Since the over-all yield of ketone has materially exceeded the molecular amount of aluminum chloride added, the later stages of the rearrangement must be brought about by aluminum chloride complexes of the ketones. The decided increase in the value for plo is significant. The data presented in Table I1 show that the o-hydroxy ketone forms much faster than the p-hydroxy ketone in the early stages of the reaction, but the rearrangement produces almost entirely p-hydroxy ketone after fifty per cent of the ester has been rearranged. Since this point corresponds molecularly to the amount of aluminum chloride added, it appears that rearrangement brought about by aluminum chloride complexes produces essentially para ketone. It appears that after the rearrangement has progressed to any appreciable extent we are dealing with at least two separate reactions, one of which orients essentially ortho and predominates in the early stages, and the

753


second of which orients para and is the dominant reaction as the rearrangement proceeds towards completion. A rearrangement of phenyl caprylate conducted for six hours a t 100" in the presence of 0.25 mole per cent of aluminum chloride gave 20.0% p hydroxycaprylophenone, 16.0% of o-hydroxycaprylophenoce, and 46.5% of phenyl caprylate. These values are in substantial agreement with those of the previous runs. When phenyl caprylate was allowed to react with an equal molecular amount of phenoxyaluminum dichloride in tetrachloroethane for six hours at loo", the product consisted of 52.0% p-hydroxycaprylophenone, 38.2% o-hydroxycaprylophenone, 5.0% phenyl caprylate, and a trace of caprylic acid. The value for p / o is 1.36. This demonstrates that phenoxyaluminum dichloride is capable of rearranging phenyl caprylate and that it gives a higher value for p / o than when aluminum chloride is used in equal molecular amounts under similar conditions, and that the value for p / o TABLE I1 REARRANGEMENT OF PHENYL CAPRYLATE BY 0.5 MOLEOF ALUMINUM CHLORIDE AT 100 SOLVENT : TETRACHLOROETHANE O.

RUN NO.

TIME (MIN.)

30 60 120 360

%PARA

10.9

19.1 31.0 41.0

I ,

1

1 ~

%ORTHO I

19.1 22.3 25.4 25.4

62.3 53.0 34.5 24.5

~

0.57 0.86 1.22 1.62

corresponds to that obtained when a deficient amount of aluminum chloride is employed. Phenyl caprylate was treated with an equal molecular proportion of the previously formed aluminum chloride salt of o-hydroxycaprylophenone in tetrachloroethane for six hours a t 100". The recovery of o-hydroxycaprylophenone was 96.4%; 58.2y0 of the original ester was recovered unchanged, and 1'3.lyOformed p-hydroxycaprylophenone. Ten and eight-tenths per cent of the ester was recovered as caprylic acid, the formation of whichis of interest and will be discussed later. It is apparent that the aluminum chloride salt of o-hydroxycaprylophenone is capable of rearranging phenyl caprylate, although it is in no wise as effective as phenoxyaluminuni dichloride or aluminum chloride. The orientation is predominantly para. b7hen phenyl caprylate reacted with an equal molecular equivalent of the aluminum chloride salt of p-hydroxycaprylophenone under similar conditions, considerable decomposition was observed. Only 70.5Yc of the original p-hydroxycaprylopherone was recovered. Twenty-one and

754

RALSTON, MCCORKLE, AND SEGEBRECHT

eight-tenths per cent of the original ester was recovered and 7.7% isolated as o-hydroxycaprylophenone. The reaction product also contained 27.3% of caprylic acid. It is evident that considerable rearrangement of the phenyl caprylate was encountered under these conditions, but because of the decomposition no definite conclusion can be drawn as to the orientation. It is apparent that the aluminum chloride salts of hydroxy ketones are capable of rearranging phenyl esters, and this accounts for yields of ketones molecularly greater than the amount of aluminum chloride employed. In order to determine the influence of the keto group alone upon this rearrangement, we treated phenyl caprylate with an equal molecular amount of a previously formed aluminum chloride complex of caprylophenone. The reaction was conducted under the same conditions as those described with the hydroxy ketones. Only 10.9% of the phenyl caprylatp was recovered unchanged. Thirty-one and eight-tenths per cent was rearranged to p-hydroxycaprylophenone, 29.5% appeared as o-hydroxycaprylophenone, and 27.6% of the ester appeared as caprylic acid. The formation of this acid is characteristic of runs in which phenyl caprylate was rearranged with 0.25 mole and 0.50 mole of aluminum chloride as well as rearrangements brought about by the aluminum chloride complex of caprylophenone and aluminum chloride salts of 0- and p-hydroxycaprylophenone. It appears that there is a direct correlation between rearrangements as brought about by ketone or hydroxy ketone complexes, and rearrangements in the presence of deficient amounts of aluminum chloride. The study of the rearrangement as brought about by the use of a molecular equivalent of aluminum chloride or less indicates that under these conditions reactions other than a splitting of an ester complex followed by an acylation must be considered. The first reaction in the rearrangement is evidently the formation of an ester-aluminum chloride complex followed by a splitting of this complex to phenoxyaluminum dichloride and acid chloride as follows: CsHSOCCTH16 + CCH60AIC12

II

0 .A1Ch

+ CrHlbCCI + AIC120CeH4COC7H16 + HC1 II

0

This splitting does not take place instantaneously, and at intermediate points we have present ester-aluminum chloride complex, phenoxyaluminum dichloride, acid chloride, and aluminum salts of the isomeric hydroxycaprylophenones. It seems probable that the acid chloride does not form an aluminum chloride complex by removing the aluminum chloride from the ester complex under these conditions, since o-hydroxy ketones are preferentially formed at the beginning of the Fries rearrangement. We

755


have previously shown (7) that high values for p l o are obtained when an acid chloride-aluminum chloride complex is present during an acylation. The Etatement that the acid chloride complex is not present under these conditions is in conformity with the findings of Xorris and Sturgis (11) who showed that by rearranging phenyl acetate with a molecular equivalent of aluminum chloride, using benzene as a solvent, no acetophenone was formed, but when two molecular equivalents of aluminum chloride were employed the formation of acetophenone was the predominant reaction. The formation of acetophenone would probably require the presence of an acid chloride-aluminum chloride complex. If splitting followed by acylation is the only reaction which occurs, we should obtain a constant value for p / o which is independent of the percentage of ester rearranged. The formation of any appreciable amount of aluminum chloride salts of hydroxy ketones will cause a competition between the ester and the ketonic group for the aluminum chloride. The formation of an irreversible ketone complex in certain acylations has been conclusively shown by many workers. If this holds for the rearrangement of phenyl esters with a molecular equivalent of aluminum chloride, it is evident that when the reaction has proceeded half way, the only aluminum chloride available to bring about further rearrangement is that attached to the hydroxyl group of the hydroxy ketone. A similar condition is encountered when less than a molecular equivalent of aluminum chloride is employed to bring about the rearrangement. We have shown that CeH50AIC12 is capable of rearranging phenyl caprylate. The following mechanism is proposed :

CsHaO

\ AlCl + C,HisCCl+ / II 0 CsHsO

C'IHISCOCBHSO

\AlCl + HC1 /

CeHs0

The aluminum chloride complex hydrolyzes to hydroxycaprylophenones and phenol. Since it has been further shown that the aluminum chloride salts of hydroxycaprylophenones are capable of rearranging phenyl caprylate, it

756


may be assumed that these rearrangements follow a similar course, thus : CaH6OCOC7H16

+ A~C~ZOC~HSCOC~HIS + CI&~SOCC~HIS I

+

O*A~C~ZOC~H~COC.IH~~

/

C~HI~COCBH~O

\

AlCl

/

C7Hi& 0CeH40’ The formation of caprylic acid in the runs previously described is possibly due to the slow rate of acylation of the intermediate complex. This reaction forms mostly para ketone and is encountered under conditions where there is a competition for the aluminum chloride, such as runs in which a molecular equivalent or less of aluminum chloride is employed, or when an aluminum chloride complex is used to effect the rearrangement. It also accounts for the observations that the amount of hydroxy ketones formed is greater than the molecular amount of aluminum chloride employed. When more than an equal molecular proportion of aluminum chloride is used in the rearrangement of phenyl caprylate, we have free aluminum chloride present in addition to the ester-aluminum chloride complex during the first part of the reaction. This permits the formation of the complex C7H15CC1.AlC13, the presence of which materially changes the reaction

II

0 mechanism. Table I11 shows the products obtained at various time intervals when phenyl caprylate is rearranged in the presence of 1.3 mole ratio of aluminum chloride in tetrachloroethane a t 100”. In addition to the compounds shown in Table 111, substantial amounts of p-caprylglphenyl caprylate were isolated and identified in the first three runs. The amount of this compound present was 9.1% in the forty second run, 10.9% in the fire minute, and 6.8% in the fifteen minute run. It was not present in the one and two hour runs. Its isolation, as an intermediate in this rearrangement, throws considerable light upon the reaction mechanism. Table IV shows the products formed when the amount of aluminum chloride is increased to two moles. It will be noted that increase in the amount of aluminum chloride greatly

757


increases the reaction rate. In the two mole run, the rate is so rapid that it is irnpossible to follow the course of the reaction. When an excess of aluminum chloride is employed, we do not observe a shift in the value of p / o as the rearrangement progresses, and it appears that the reaction mechanism differs from runs where a deficient amount of aluminum chloride is used. It is believed that when substantially more than one molecular equivalent of aluminum chloride is employed the mechanism of the rearrangement of phenyl. caprylate is as follows:

+

( ~ ~ H ~ O C C ~ HAlC1.y I ~ + CeHEOAlC12

II

+ CrK16CCl-AlCls II

-

0

O AlC&

TABLE I11 REARRANGEMENT OF PHENYL CAPRYLATE BY 1.3 MOLESOF ALUMINUM CHLORIDE AT 100". SOLVENT: TETRACHLOROETHANE R G N NO.

1

TIME (MIN.)

110 11 12

13 14

40 8ec. 5 120

I

1

%PARA

3.64 23.2 33.2 54.5

1

%

ORTHO

0.0

12.3 16.8 28.9 30.1

I

%

ESTER

81.5 52.3 39.5 19.3 12.6

1.88 1.97 1.71 1.81

The reaction then follows one of two courses: 1. The phenoxyaluminum dichloride may be acylated, thus: C61&0AlC12

+ C7HlaCOCl. A1CL -+ A ~ C ~ ~ O C ~ H ~fC CHC1 ~HI~ II

0 * AlC13 2. The ester may be acylated and this product reacts with phenoxyalumirmm dichloride, thus:

The more ester present, the greater the probability of the second mechanism, which means that it is the dominant reaction in the early stages of the rearrangement.

758


I n order to study further this second mechanism, 0.05 mole of p-caprylylphenyl caprylate was reacted with 0.05 mole of phenol and 0.13 mole of aluminum chloride for six hours a t 100" in tetrachloroethane. This resulted in the formation of 83.6% p-hydroxycaprylophenone and 15.9% o-hydroxycaprylophenone. The theoretical yield of para isomers which could be formed by scission of the p-caprylylphenyl caprylate is 50%. The acylation of the phenol, therefore, under these conditions resulted in 33.6y0 of p- and 15,9% of o-hydroxy ketones and the value for p/o is 2.1 which indicates that there is a preference for the formation of the para isomer. That p-caprylylphenyl caprylate is an intermediate in the rearrangement of phenyl caprylate where excess aluminum chloride is employed is shown by a run in which phenyl caprylate was brought into reaction with two moles of aluminum chloride for 30 minutes a t 50". The products consisted of 17.7% p-hydroxycaprylophenone, 17.0% o-hydroxycaprylophenone, 39.1% phenyl caprylate, and 18.6% p-caprylylphenyl caprylate. KOo-caprylylphenyl caprylate was isolated in any of the runs.

TABLE IV REARRANGEMENT OF PHENYL CAPRYLATE B Y 2.0 MOLES OF ALUMINUM CHLORIDE AT 100". SOLVENT: TETRACHLOROETHANE R U N NO.

TIME (MIN.)

15

5

16

15

%PARA

55.5 56.0

%

PI0

ORTHO

1.44 40.0

0.9

1.40

In another run 0.1 mole of phenyl caprylate was added to 0.1 mole of aluminum chloride in tetrachloroethane and to this was added 0.1 mole of caprylyl chloride and 0.1 mole of aluminum chloride. We thus have present an ester-aluminum chloride complex and a caprylyl chloride-aluminum chloride complex. The product consisted of 10.1% o-hydroxycaprylophenone, 12.1% p-hydroxycaprylophenone, 7.2% caprylic acid, 2.3% phenyl caprylate, and 52.0% p-caprylophenyl caprylate. In a previous paper we stated that o-hydroxycaprylophenone did not rearrange to p-hydroxycaprylophenone when heated for six hours with two moles of aluminum chloride at 100" in the presence of tetrachloroethane, and that the para isomer does not rearrange to the ortho isomer under similar conditions. The work of Eykmann (12), Rosenmund and Schnurr (S), and Stoughton (13) shows that high temperatures favor the formation of para isomers. Rosenmund and Schnurr rearranged p-acetylcresol to o-acetylcresol by heating the former for 30 minutes a t 170" and Stoughton showed that 4-acetylnaphthol rearranged to 2-acetylnaphthol when heated with an equal weight of aluminum chloride for three hours

759

THE FRIES REARRAN'GEMENT

a t 100-120". It seems probable that the value for p / o is dependent to some extent on the temperature, since in the rearrangement of phenyl caprylate there have been shown to be at least two simultaneous reactions, the products of which do not have similar values for the ratio p / o . We have, therefore, investigated the effect of temperature upon the rearrangement of phenyl caprylate in the presence of aluminum chloride. Table V shows the effect of temperature upon the rearrangement of phenyl caprylate in the presence of an equal molecular proportion of aluminum Izh1orid.e. Although it has been observed that data concerning the effect of a reaction condition upon orientation must be compared at substantially the same percentage conversion of the ester, it is apparent that the value for p / o is higher a t the lower temperature than a t 100'. It appears, therefore, that low temperatures favor the formation of p-hydroxy ketones in the rearrangement of phenyl caprylate. That this is not due to a rearTABLE V TEMPERATURE UPON THE REARRANGEMENT OF P H E N Y L CAPRYLATE WITH ON:EMOLERATIOOF ALUMINUM CHLORIDE.SOLVENT: TETRACHLOROETHANE

E F F E C T OF

R U N NO,

--

TEMP., 'C.

15' 18

25 50

19

50 100

I

TIME

7 days 8 hrs. 30 hrs. 15 min.

% PARA

% ORTHO

% ESTER

PI0

5.9 4.5 17.7 8.6

7.7 8.2 20.0 18.2

81.4

0.76 .55

77.8 51.0 66.0

.88

.47

rangeinent of p-hydroxycaprylophenone to o-hydroxycaprylophenone is shown by the fact when 0.1 mole of p-hydroxycaprylophenone was refluxed with 0.13 mole of aluminum chloride in tetrachloroethane for two hours a t 146" the recovery of p-hydroxycaprylophenone was 99.6%. When 0.1 mole of p-hydroxycaprylophenone was heated with 0.13 mole of aluminum chloride a t 180" for three hours, the product consisted of 59% 0- and 10.5% p-hydroxycaprylophenone and 21.7% residue. Rearrangement of p-hydroxycaprylophenone to the ortho isomer, therefore, takes place :at temperatures above 146". It appears that tetrachloroethane does not influence orientation, since when 0.1 mole of phenylcaprylate was rearranged with 0.13 mole of aluminum chloride a t 100"for six hours in the absence of a solvent we obtained 64% para- and 34.6% ortho-hydroxycaprylophenone, which gives a value for p/o of 1.85. This value is in agreement with the value of 1.81 obtained when this ester was rearranged in the presence of tetrachloroethane under similar conditions (Run 14). When phenyl caprylate was rearranged in the presence of 0.1 mole of alumi-

760


num chloride in the absence of a solvent, the product consisted of 24.0% of p-hydroxycaprylophenone and 63.5% of the ortho isomer. The increase in temperature from 100" to 190" greatly increased the percentage of ortho isomer. EXPERIMEXTAL

The following procedures are typical examples of runs reported in this article. Fries rearrangement of phenyl caprylate. Phenyl caprylate (22 g., 0.1 mole) prepared as previously described (7) was dissolved in 60 cc. of tetrachloroethane and the mixture placed in a three-necked flask, equipped with a mechaniwl stirrer and thermometer. The solution was heated t o 80" and aluminum chloride (13.3 g., 0.1 mole) added. The reaction mixture was heated for six hours a t 100" after which i t was hydrolyzed, steam distilled and the isomers separated and analyzed as previously described (7). In those runs in which p-caprylylphenyl caprylate appeared, i t was separated from the ortho ester fraction by fractional distillation. The compound was identified by mixed melting point with an authentic sample. Reaction of phenyl caprylate with phenoxyaluminum dichloride. Phenol (9.4 g., 0.1mole) was dissolved in 50 cc. of tetrachloroethane and aluminum chloride (13.3g., 0.1mole) waa added. The mixture was heated a t 100" until hydrogen chloride ceased t o be evolved. Phenyl caprylate (22g., 0.1 mole) was added and the mixture heated for six hours at 100". The product was hydrolyzed, steam distilled, and the isomers separated as previously described. The excess phenol was removed during the steam distillation. The product consisted of 11.5 g. (52%) of p-hydroxycaprylophenone, 8.4 g. (38.2%) of o-hydroxycaprylophenone, 1.1 g. (5.0%) of phenyl caprylate, and a trace of caprylic acid which was separated from the para fraction. The caprylic acid was separated from p-hydroxycaprylophenone by fractional distillation and was identified as the diamide of 4,4'-diaminodiphenylmethane,m.p. and mixed m.p. 182-183' (14). Reaction of phenyl caprylate with the aluminum chloride salt of o-hydroxycaprylophenone. o-Hydroxycaprylophenone (22 g., 0.1 mole) was dissolved in 50 cc. of tetrachloroethane and aluminum chloride (13.3 g., 0.1 mole) added. There was a considerable evolution of hydrogen chloride during the addition of aluminum chloride. After heating to 100' for a short time to complete the reaction, phenyl caprylate (22.0 g., 0.1 mole) was added and the mixture heated for six hours a t 100". The product was treated in the usual manner. Ninety-six and four-tenths per cent of the o-hydroxycaprylophenone was recovered unchanged and also 58.2% of the phenyl caprylate. The yield of p-hydroxycaprylophenone was 19.1%. An additional 10.8% of phenyl caprylate mas recovered as caprylic acid. Reaction of phenyl caprylate with the aluminum chloride salt of p-hydroxycaprylophenone. The same procedure was used in this experiment as in the preceding example except that the o-hydroxycaprylophenone was replaced by p-hydroxycaprylophenone. Seventy and five-tenths per cent of the p-hydroxycaprylophenone was recovered unchanged together with 21.8% of the original ester. The yield of o-hydroxycaprylophenone was 7770. Caprylic acid (27.3%) was also recovered. Reaction of phenyl caprylate with aluminum chloride-caprylophenonc complex. Caprylophenone (20.3g., 0.1 mole) was dissolved in 50 cc. of tetrachloroethane and aluminum chloride (13.3g., 0.1 mole) added. After heating t o loo", phenyl caprylate


761

(22.0g.,0.1 mole) was added and the heating continued for 6 hours. The product was treated in the customary manner. The mixture of phenyl caprylate, o-hydroxycaprylophenone and caprylophenone obtained after removing the para ketone and caprylic acid with sodium hydroxide was distilled. The residue (10 g., 49.5%) was assumed to be a decomposition product of the complex, aluminum chloride-caprylophenone. Ten and nine-tenths per cent of the ester was recovered unchanged and 27.6% appeared as caprylic acid. The yield of p-hydroxycaprylophenone was 31 2% and t h a t of o-hydroxycaprylophenone 29.5%. Preparation of p-caprylylphenyl caprylate. p-Hydroxycaprylophenone (22.0 g., 0.1 mole) was heated with caprylyl chloride (18 g., 0.11 mole) t o approximately the boiling point of caprylyl chloride for one hour. The product was distilled; a small amount of caprylyl chloride came over followed by 33 g. (95%) of the ester, b.p. 215-225"/1 mm., which solidified upon standing. Upon crystallization from either ethanol or petroleum ether (b.p. 60-68")the m.p. was 56.5-57.5". Anal. Calc'd for CzzHsrO$:C, 76.9;H, 10.2. Found: C, 77.0;H, 10.4. Reaction of p-caprylylphenyl caprylate with phenoxyaluminum dichloride. p-Caprylylphenyl caprylate (17.3,0.05mole) was dissolved in 50 cc. of tetrachloroethane together with phenol (4.7g., 0.05 mole), and aluminum chloride (13.3g., 0.1 mole) was added. The reaction was heated for six hours at 100" and the products isolated as previously described. The following yields of products were obtained: p-hydroxycaprylophenone 18.4 g. (83.6%) and o-hydroxycaprylophenone 3.5 g. (15.9%). Reaction of caprylyl chloride with phenyl caprylate. Phenyl caprylate (22.0 g., 0.1 mole) was dissolved in 50 cc. of tetrachloroethane and aluminum chloride (13.3g., 0.1 mole) added. During the addition of the aluminum chloride there was a continuous temperature rise from 27" to 55". Caprylyl chloride (16.2g., 0.1 mole) was added rapidly. No temperature rise was observed during this addition. An additional 13.3g. (0.1mole) of aluminum chloride was now added and the reaction heated for 3 hours a t 90-95". The product was hydrolyzed and the isomers separated in the manner previously described. The yields were as follows: p-caprylylphenyl caprylate 18.0 g. (52.0%), o-hydrosycaprylophenone 3.0g., (13.6%), phenyl caprylate 0.8 g. (3.6%), caprylic acid 2.5 g. (8.7%), and p-hydroxycaprylophenone 4.2 g. (19.1%). From the alkali-soluble fraction there was isolated in addition to caprylic acid and p-hydroxycaprylophenone a material (3.1 g., 8.9%), b.p. 205-220"/1 mm., which was considered to be a hydroxy diketone. Attempted rearrangement of p-hydroxycaprylophenone. p-Hydroxycaprylophenone (22.0g., 0.1mole) was dissolved in 50 cc. of tetrachloroethane, and aluminum chloride (17.5g., 0.13 mole) added. The reaction was refluxed for 2 hours, hydrolyzed, and steam distilled to remove the tetrachloroethane. From the residue by alkali extraction was isolated 21.9 g. (99.0%) of p-hydroxycaprylophenone. Under similar conditions o-hydroxycaprylophenone was recovered unchanged, (20.5 g;., 93.00/0). Rearrangement of p-hydroxycaprylophenone. p-Hydroxycaprylophenone (22.0g., 0.1moje) was heatedwith aluminum chloride (18.3g., 0.1mole) for 1 hour a t 170-190". The reaction product was treated in the usual manner. From the product was isolated 51.3 g. (10.5%) of p-hydroxycaprylophenone, and 13 g. (59.0%) of o-hydroxycapryluphenone. The 2,4-dinitrophenylhydrazone of the ortho ketone melted a t 143-144" alone or mixed with an authentic sample (15). Rearrangement of phenyl caprylate without solvent (170-190°). Phenyl caprylate

762


(22.0 g., 0.1 mole) mas heated with aluminum chloride (17.3 g., 0.13 mole) for 1 hour a t 170-190". The reaction mixture mas then cooled, hydrolyzed, and the isomers separated as previously described. p-Hydroxycaprylophenone (5.3 g., 24%) and o-hydroxycaprylophenone (14.0 g., 63.5%) were isolated. Rearrangement o j phenyl caprylate without solvent (90-fOOo). The above reaction was conduct,ed at 90-100" for 4 hours. The yield of products was, p-hydroxycaprylophenone 14.1 g., (64.0%) and o-hydroxycaprylophenone 7.6 g., (34.6%). SUMMARY

1. A study of the partially completed and completed rearrangements of phenyl caprylate in the presence of varying molecular proportions of aluminum chloride has been made. Phenyl caprylate was rearranged by means of the various aluminum chloride complexes which were considered likely to be present in the rearrangement of phenyl caprylate. 2. When approximately equal molecular proportions or less of aluminum chloride are used to effect the rearrangement, the value of p / o increases as the reaction progresses. 3. The molecular amount of ester rearranged is greater than the molecular equivalent of aluminum chloride employed if the amount of aluminum chloride is less than a molecular proportion. 4. Phenoxyaluminum dichloride, the aluminum chloride salts of 0- and p-hydroxycaprylophenone, and the aluminum chloride complex of caprylophenone bring about the rearrangement of phenyl caprylate. 5. When substantially more than molecular proportions of aluminum chloride are employed, the ratio of isomers is essentially independent of the amount of ester rearranged. p-Caprylylphenyl caprylate has been identified as an intermediate when sufficient aluminum chloride is present to form the caprylyl chloride-aluminum chloride complex. 6. Temperatures above 140" favor the formation of o-hydroxycaprylophenone. p-Hydroxycaprylophenone rearranges to o-hydroxycaprylophenone a t 180". i . Some suggestions as to the various mechanisms involved have been proposed. CHICAGO,ILL.

REFERENCES (1) SANDULESCO AKD GIRARD, Bull. S O C . chim., 47, 1300 (1930).

(2) (3) (4) (5) (6)

PERRIER, Ber., 33, 815 (1900). B~ESEKEN Rec. , trav. chim., 39, 623 (1920). KOHLER,Am. Chem. J.,24, 385 (1900). OLIVIER,Rec. trao. chim., 37, 205 (1918). GROGGINS, Ind. E n g . Chem., 23, 152 (1931).

THE FRIES REARRA4NGEXENT

(7) RALSTON, MCCORKLE, AND BACER, J . Org. Chem., 6, 645 (1940). AND SCHNURR, Ann., 460,56 (1928). (8) ROSENMUND AND POLLER, Ber., 67, 2033 (1924). (9) SKRAUP (10) Cox, J . Am. Chem. SOC.,62, 352 (1930). (11) ?

ORIENTATION IN THE FRIES REARRANGEMENT OF PHENYL

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