S Y N T H E S I S AND I S O M E R I Z A T I O N OF 2 - N - P R O P Y L - 5 - P H E N Y L T E T R A H Y D R O F U R A N

(UDC 547.72)

N. I . S h u i k i n , I . A p ' o k , M. B a r t o k , I . F. B e l ' s k i i , a n d R. A. K a r a k h a n o v

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences, USSR Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. '/46-747, April, 1964 Original ar t ic le submitted August 12, 1963

In our previous works [1-3], we described the synthesis of 2,4- and 2 ,5-d ia lky l - and 2,3 ,5- t r ia lkyl-subst i tuted homologs of tetrahydrofuran. The synthesis was based on the reaction of ca ta ly t i c hydrogenation of y-furyla lkanols

in the vapor phase. Depending on the structure of the carbon side chain, various homologs of tetrahydrofuran are ob- tained. The lat ter , as is well known, are easily isomerized, best of all on a plat inum catalyst , to a l iphat ic carbonyl compounds [4, 5]. The method we found for synthesizing homologs oftetrahydrofuran was used in this work to pro- duce 2-n-propyl-5-phenyl te t rahydrofuran according to the following scheme

~ H2 ~, 120" CH0 + CH.,q~c.4Bs ~ C.H..-------~H--~C~FI5 Cu2CrO4

--..IF-i] u~,~-c r n l--'-I

OH - L o~ oH _1

The isomerizat ion of 2-n-propyl-5-phenyl te t rahydrofuran was conducted on P t - C at 300 ~ Opening of the ring occurred in both direction, but mainly at the C - O bond next to the phenyl radical . As a result, 48% 1-phenyl- heptanone-4 was formed. In the other d i r e c t i o n - a t the C - O bond next to the propyl radical , the ring was opened to an extent of only 12%; in this case n-hexyl phenyl ketone was formed:

C--C--C~C~H5

7 C--C--C--C--C--C--C--C6H ~ C--C--C--~--C--C--C--C6H5

II O O

We should mention that, in contrast to tetrahydrofuran homologs, the isomerizat ion of 2 -n -p ropy l -5 -pheny l - tetrahydrofuran proceeds less smoothly, since in this case a considerable amount of high boi l ing products isformed.

E X P E R I M E N T A L

Synthesis of Furfurylideneacetophenone. Acetophenone (200 g), furfural (160 g), and 350 ml of absolute a l - cohol were p laced in a th ree-necked flask, equipped with a thermometer, dropping funnel, and mechanica l mixer. A solution of 30 g sodium ethylate in absolute alcohol was added over a period of 3.5 h with cooling to 0 ~ On the next day 300 ml of water was added to the react ion mixture, and then the mixture was neut ra l ized with 50% ace t ic acid. The organic layer was removed, dried, and disti l led under vacuum: b.p. 180" (11 mm), y ie ld 7 0 % o f

the theoretical .

Synthesis of 1-( c~-Furyl)-3-phenylpropanol-3. Into a 1- l i ter autoclave were loaded 200 g furfuryl ideneaceto- phenone, 250 ml of prel iminary redist i l led dioxane, and 35 g of a copper-chromium catalyst; the mixture was heated to 120-130 ~ Initial hydrogen pressure was 120 atm. Hydrogenation was ended after the absorption of 60 liters of

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hydrogen. The catalyzate was freed of the catalyst by Nitration, and after distil lation of the dioxane, the residue

was filled under vacuum. The 1- (a- fury l ) -a -phenylpropanol -a obtained boiled in the range 160-162 ~ (10 ram) and

possessed riD2~ 1.5460 and d42~ 1.1012, its yield was 70% of the theoretical.

Catalyt ic Hydrogenation of 1-(a-Furyl) -3-phenylpropanol-3 in the Vapor Phase. The ca t a lys t -p l a t in i zed

carbon (10% Pt) was prepared by impregnating activated birch charcoal with a solution of chloroplatinic acid, fol- lowed by reduction with hydrogen in the catalyt ic reaction tube, gradually raising the temperature to 300 ~ . At this

temperature, reduction occurred in 10 h. The catalyst was placed in a quartz tube in amounts of 50 rot. Hydrogena-

tion was conducted at a temperature of 220 ~ The catalyzate obtained after two-hour passage of l - ( a - f u r y l ) - 3 - phenylpropanol-3 at a space velocity of 0.1 h -1 was distilled on an efficient column. The following fractions were

obtained at a pressure of 3 m: 1 - 9 3 - 9 5 ~ 28 g, nD 2~ 1.5298; I I - 9 5 - 1 0 5 ~ 19 g, nD ~ 1.8270; I I I - -105-108 ~ 42 g,

nD2~ 1.5238; I V - 1 0 8 - 1 2 6 ~ 22 g, nD ~ 1.5410; V - 1 2 6 - 1 3 1 ~ 59 g, nD ~" 1.5470.

Fractions I-III obviously represented a mixture of the cis- and trans-forms of 2-phenyl-5-n-propyl te t rahydro-

furan. This was confirmed by the results obtained in an analysis of these fractions by the method of gas-l iquid chro-

matography, as well as by elementary analysis. For ClaHtsO calculated: C 82.05; H 9.53% Found: C 82.32; H

9.28% Fractions IV-V represented mainly the uncoverted 1-(a-furyl)-3-phenylpropanol-3.

Isomerization of 2-n-Propyl-5-phenyltetrahydrofuran. 2-Phenyl-5-n-propyltetrahydrofuran was passed twice

over p la t in izedcarbon at 300 ~ The catalyzate, obtained in more than 90% yield, was distilled on a column. In

this case we isolated 1-phenylheptanone-4 (48%), b.p. 115-116" (4 ram); 111:)~ 1.4974; n-hexyl phenyl ketone (10%),

b.p. 121-122" (5 ram); nD 2~ 1.5068, semica rbazone-m.p . 117 ~

S U M M A R Y

1. The synthesis of 2-n-propyl-5-phenyltetrahydrofuran was accomplished by catalyt ic hydrogenation of 1- furyl-3-phenylpropanol-3 in the vapor phase on P t - C at 220 ~

2, 2-n-Propyl-5-phenyltetrahydrofuran is isomerized on P t - C at 300 ~ with opening of the ring at b o t h C - O

bonds: 48% at the bond next to the phenyl radical, and 10% at the bond next to the propyl radical.

L I T E R A T U R E C I T E D

1. L F. Bel'skii and N. I. Shuikin, Dokl. AN SSSR 128, 945 (1949). 2. N. I . Shuikin and I. F. Bel'skii, Dokl. AN SSSR 137, 622 (1961). 3. L F. Bel'skii and N. I. Shuikin, Izv. AN SSSR, Otd. Khim. N. 1962, 1656.

4. N. I . Shuikin and I. F. Bel'skii, Dokl. AN SSSR 120, 548 (1958).

5. N. I . Shuikin, I. F.Bel'skii, and R. A. Karakhanov, Dokl. AN SSSR 12% 815 (1959).

All abbreviations of periodicals in the above bibliography are letter-by-letter transliter- at.ions of the abbreviations as given in the original Russian journal, Some or all of t h i s peri-

od ica l l i t e ra ture m ay we l l be a v a i l a b l e in E n g l i s h t rans la t ion . A complete list of the cover-to- cover English translations appears at the back of this issue.

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