547.318.81 PROOF OF THE CONSTITUTION OF CETENE

BY

N. SCHOORL.

It has been shown by a refractometric method that the double bond is really situated in the terminal position in cetene prepared by L a n g e d if k and S t e d e h o u d e r .

L a n g e d i j k and S t e d e h o u d e r 1) have recently supplemented K r a f f t ' s constitutional proof from which it appears that the hydro- carbon C,,H,,. obtained by distillation of cetyl palmitate ( spermaceti) under reduced pressure and called cetene, is actually 1 -hexadecene.

They do not state that E y k m a n 2 ) believed he had demonstrated the terminal position of the double bond in cetene in quite a different way, namely by comparison of the molecular refraction with that of hex ad eca n e .

Since the difference in the influence of the terminal and the non- terminal double b o d on the molecular refraction is only small and thus one is here dealing with minute differences, objections can be made to E y k m a n ' s proof, namely ( 1 ) that he employed cetene of not quite definitely established purity,. i.e. obtained by freezing out commercial cetene and ( 2 ) that he deduced the molecular refraction of the htrxadecane required for the comparison by a calculation about which E y k m a n has given no details.

It is therefore indeed desirable to compare L a n g e d ij k and S t e d e h o u d e r ' s cetene. which is probably very pure 3) with the saturated hydrocarbon CIBH,, by means of E y k m a n ' s method, as the data for the latter can be deduced with greater certainty than formerly from tshe measurements of S h e p a r d and his coworkers 4 ) . Undeniably this proof would be still better by preparing

l) S. L. L a n g e d l j k and P. L. S t e d e h o u d e r , Rec. trav. chim. 56, 526-

2, J. F. E y k m a n, Chem. Weekblad 3, 714 (1906). 3, Their preparation was kindly placed at my disposal by Messrs. L a n g e d ij k

4, A. F. S h e p a r d and his coworkers, J. Am.

528 (1937).

and S t e d e h o u d e r . Chem. SOC. 53, 1948 (1Y31).

720 N. Schoorl.

this hydrocarbon C,,H,, by hydrogenation of the cetene for comparison.

The difference in the influence of the terminal and non-terminal double bond on the molecular refraction has first to be established.

T o determine the refractometric equivalent of the double bond one can use only very accurate measurements of substances of great purity and in which the double bond is separated from the terminal H or other atomic groups by at least two (preferably more) CH,

groups. I shall only employ the form m.- for the molecular

refraction following G 1 a d s t o n e and D a 1 e (1 863) and only take sodium D-light into account. E y k m a n ' s measurements are here worthy of consideration in the first place since they are among the most accurate which have been carried out. They were mosdy made with the hydrogen lines, sometimes (in later years) with the helium lines, but these can be recalculated to those for D-light by means of C a u c h y ' s formula.

The refractometric equivalent of the terminal double bond CH, = CH-.

By a comparison of the unsaturated compound with the corres- ponding saturated one, it is possible to calculate the influence which the removad of 2 H and the substitution for it of the double bond has on the molecular refraction. I shall indicate this refractometric equivalent by [-2 HI following E y k m a n ' s ideas.

Diallyl, C,H,,, with two terminal double bonds, was measured by E y k m a n (I.c. p. 706) at 15.9' and can be compared 5 ) with hexane, which has been prepared very pure and accurately measured by S h e p a r d (1. c.) at 20'. By subtraction one finds twice [- 2 HI.

A,-Pentenic acid, C,H,O,, was measured by E y k m a n at 17.7O and at 77.9'. so that the result can be interpolated to 20' and com- pared with that of n-valeric acid at 20'. also measured by E y k m a n (1.c.) but also very accurately by T i m m e r m a n s and H e n n a u t- R o 1 a n d 6) .

This unsaturated acid has also been investigated again later by

6 ) The specific refraction 5' and the molecular refraction calculated from it

only change but little with the temperature, and in general become 0.005 70 lower for 1" rise in temperature so that diallyl with a mol. refr. of about 48 would only fall by 1 in the second decimal on recalculation from 15.9" to 20".

e, J. T i m m e r m a n s and h e H e n n a u t - R o l a n d , J. chim. phys. 29, 529 (1932).

n - 1 d

~~

Proof of the constitution of cetene. 72 1

E y k m a n 7 ) under the name allylacetic acid at 16.85'. which result can also be recalculated to 20'.

A,-Undecylenic acid, C,,H,,O,, is to be found in E y k m a n ' s later investigations * j , investigated at 34.6' and can be compared with the saturated undecylic acid, accurate data for which can be calculated for 30' from the determinations of G a r n e r and R y d e r e ) and those of W a t e r m a n and B e r t r a m ' o ) .

A,-n.Ocfene, C,Hl,, has been prepared very pure by W a t e r- m a n and d e K o k 11) and measured at 20'. as also the octane C,H,, prepared from it by hydrogenation.

The results are then:

Dkllyl 47.79 Al-Pentenic acid 43.84 nl-Pentenic acid 43.84 -n . Valeric acid (T.) 44.34

- 1.12 - 0.56 - 0.50 -Helane 48.91 --n. Valeric acid (Ey.) 44.40

__

Allylacetic acid 43.83 Allylacetic acid 43.83 - n. Valeric acid (Ey.) 44.40 - n. Valeric acid (T.) 44.34

- 0.57 - 0.51

A,-Undecylenic acid (30°) 90.62 A!-n. Octene 63.99 n. Octane 64.51

.~ Undecylic acid (No) 91.13

- 0.5 I - 0.52

The mean result of these observations gives for the terminal double bond

[- 2H] = - 0.54.

The refracfomefric equivalent of the non-terminal double bound

A,-Hexylene, C,Hl,, has been measured by E y k m a n (1. c.

, thus 48.80 n-1 p. 706) at 16.0° and gives the value 48.81 for m. __ d

at 20'. W e must compare this with hexane, which was indeed investigated by E y k m a n 12) but his preparation was not sufficiently

') J. F. E y k m a n , Oeuvres posthumes, publ. by A. F. H o l l e m a n 1919.

J. F. E y k m a n, Ibid.. p. 494. For m. - in D-light one finds 90.60 at 34.6",

-CH = CH-.

p. 492.

which reduced to 30" becomes 90.62.

n -1 d

9) W. E. G a r n e r and F. A. R y d e r , J. Chem. Soc. 127, 728 (1925). 10) H. I. W a t e r m a n and S. H. B e r t r a m , Rec. trav. chim. 46, 701 (1927). 11) H. I. W a t e r m a n and W. J. C. d e K o k . Rec. trav. chim. 53, 725-729

12) J. F. E y k m a n , Rec. trav. chim. 14, 187 (1895). (1934).

722 N . Schoorl.

pure and gives 49.00 at 20'. It is meanwhile the result from this preparation which E y k m a n ( 1906) himself uses as the basis of his calculations. It would give us the equivalent 0.20 for D-light. E y k m a n 13) measured hexane once more at 15.45', from which

=48.94 follows, which would thus give an equivalent -0.13.

W e would prefer to insert S h e p a r d ' s (1. c.) more accurate vdue mentioned above.

A,-Octylene. C,H,,, was measured by E y k m a n (1. c.) at 20' n-1 and gives the value 64.36 for rn. -. Compared with octane, which

d was also measured earlier by E y k m a n 1 4 ) and furnishes 64.64, the equivalent [- 2 HI would become - 0.28, which is certainly too large. It is better to use the result of the more accurate determination of S h e p a r d (1. c.) for octane in this case also.

A,-Hexenic acid and A,-Hexenic acid, C,H,,O,, have both been measured by E y k m a n (1. c.) at 21O and 22.6' respectively and

furnish for m.-the values 51.98 and 52.00 respectively. The result

for the hexylic acid to be compared with it was calculated by E y k m a n from his value for valeric acid (see above). It is better to substitute the value determined directly with pure capric acid, C,H,,O,. The first series of data given below are due to S c h e y 15)

(1899), the second were determined by me with a pure specimen from K a h l b a u m (eq. 116.2).

t d no

n-1 m.d

n-1 d

n-1 n-1 d

20 0.9274 1.41635 0.4490 52.08

- d

20 0,928 1 1.41659 0.4489 52.07

Elaidic acid, C,,H,,O,, was measured later by E y k m a n 16) at

80.5' C and furnishes 145.36 for rn. - .This result must be com-

pared with that of stearic acid at 80°, the two observations for which by E y k m a n ( 1893 and posth.) do not agree well with one another, giving 145.32 and 145.40 resp. I therefore substitute for them the

18) J. F. E y k m a n . Oeuvres posthumes, publ. by A. F. H o l l e m a n . 1919,

la) J. F. E y k m a n, Chem. Weekblad 3, 655 (1906). 16) L. T. C. S c h e y , Rec. trav. chim. 18, 183 (1899). 18) J. F. E y k m a n , Oeuvres posthumes, publ. by A. F. H o l l l e m a n , 1919.

n-1 d

p. 441.

p. 494.

Proof of the constitution of cefene. 723 ~-~

results found by myself with V i s s e r ' s pure stearic acid (18%). as follows:

n-1 n- 1 __ d 7- t C l nu

80.0 0.8 394 1.4299 0.5121 145.46

Finally A,-Undecylenic acid can be used, measured by E y k- m a n 17) at 24' and at 79.7' and which furnishes the value 91.08 for

n- I m.-by interpolation to 20'. This must be compared with undecylic d acid which has already been explained.

The results are then: &Hexylene 48.80 &-Octylene 64.36 nz-Hexenic acid 51.98 - Hexane 48.91 -Octane 64.51 - Capric acid 52.08

-- 0.1 1 - 0.15 - 0.10 ~-

&-Hexenic acid 52.00 Elaidic acid 145.36 &-Undecylenic acid 91.08 - Capric acid 52.08 - Stearic acid 145.46 - Undecylic acid (20O) 91.15

-- 0.08 - 0.10 - 0.07

The mean result of these observations gives for the non-terminal double bond

[- 2 HI = - 0.10.

There thus exists a sufficient difference in the value of the refractometric equivalent for the terminal and the non-terminal double bond to be able to decide for cetene whether its constitution corresponds or not with hexadecene-1 , provided accurate deter- minations are made with a very pure preparation and the mdecufar refraction of n-hexadecane, C,,HS,. is established.

This latter point must be dealt with first. E y k m a n carried out measurements on the normal saturated hydrocarbons, C,, to C,, and as a rule in the neigh.bourhood of 40' and of 80°; but just not for C,,H,,. Since this latter hydrocarbon borders immediately on the series investigated, the value for C,,HS, could however safely be found by extrapolation, as E y k m a n (1906) has in fact done (see above).

In order to be able to make these extrapolations rationally. let us consider 16) the specific refraction as a linear function of the reciprocal

17) J. F. E y k rn a n, Rec. trav. chim. 12, 62 (1893) and Chem. Weekblad 3, 713

I*) N. S c h o o r 1, Chem. Weekblad 22, 249 (1925). (19o6).

N. Schoorl. - 724

- -~ . - -

0.5620 0.5623 -3 0.5603 0.5603 0.5623 0.5621 + 2 11 0.5601 0.5601 0.5619 0.5618 + 1 0.5599 0.5599 0.5612 0.5616 -4 0.55% 0.5597 0.5612 0.5613 -1 0.5595 0.5595

0.5611 0.5610 + 1 , 0.5592 0.5593 0.5615 0.5611 + 4 0.559i 0.559i

of the molecular weight. When we then recalcullate all the observations of E y k m a n on the above mentioned series of hydro- carbons to D-light and extrapolate to 20' and 80°, the following

linear functions can be deduced from the values he found for - * d '

n - 1

0 0 0

-1 0

-1 0

r$) = 0.5571 + 1.255 X I/m. 10

(!!!!) = 0.5563 + 0.955 X l/m. 80

It can be seen from the table given below in how far the result of these formulae agree with E y k m a n ' s observations.

It is clear that the observed series at 80' forms a much better linear function than that at 20°, which is not surprising since the temperature 20' lies far outside the temperatures of observation.

The observations of E y k m a n (1. c.) on his cetene, recalculated to D-light give:

n-1 n - 1 m. - d d

- t d nD

1 i.6 0.78i9 1.4i368 0.56527 126.62 79.8 0.7394 1.41654 0.56335 126.19

If we interpolate this result ,to 20' and 80' and compare there- with the calculated values for hexadecane according to the formulae given above:

C16H32 = 221 Hexadecane Cl& = 226 [ -2Hl n-1 n-1 n-1 n-1

m. - d m.- d d d - t

200 0.56513 126.59 0.5627 127.17 -0.58 80° 0.56335 126.19 0.5605 126.68 - 0.49

then the result for [- 2 HI is definitely favourable to the terminal double bond.

Proof of the constitution of cetene. 725

However the cetene of E y k m a n was certainly not so pure a s that prepared by I, a n g e d ij k and S t e d e h o u d e r.

I made the following observations on this latter speci.men. Pro- visional determinations of the specific gravity with the Mulliken- pipette gave d,, = 0.7824 and of the refraction with the Zeiss-Abbe total-refractometer n t: = 1.441 5.

Accurate determinations were carried out in the neighbourhood of 15'. 20' and 25'. for the specific gravity with the Adams-Johnston pyknometer and for the refraction with the Eykman refractometer. Recalculated to precisely 15', 20' and 25' they gave the folbwing values:

n - 1 n- 1

15 0.78577 1,44360 0.5545 126.46 20 0.78233 1.44145 0.5643 126.40 25 0.77889 1.43930 0.5640 126.31

Instead of comparing this result with the molecular-refraction of hexadecane at 20' calculated by E y k m a n, it is better to calculate the latter from measurements of S h e p a r d (1. c.) on a series of normal saturated hydrocarbons, carried out at 20'. These gave values for the specific refraction which satisfy the linear function

d - .-

d t d n D

= 0.5571 + 1.01 X I/m, 20

with much greater accuracy than the E y k m a n series extrapolated to 20'. -

m

. . ~

72 86

100 114 128 142 156 170

found

0.571 1 0.5687 0.5671 0.5658 0.5651 0.5643 0.5637 0.5630

. . .. - .. ___._.__

n - 1 d - calc.

0.571 1 0.5688 0.5672 0.5660 0.5650 0.5642 0.5636 0.5630

__ n ____ 0

- 1 -1 - 2 + 1 + 1 + 1 0

O n the basis of this formula one can calculate for hexadecane.

C,,H3,: m = 226 . _. . = 0.5616, n-1 d

n-1 d

irom which follows rn . = 126.92.

726 N. Schoorl. Proof of the constitution of cetene.

If one were to use this much more trustworthy result for hexa- decane for comparison with Ey k m a n ’ s result for cetene then the result:

would leave open the question whether the double bond is in the terminal position or not.

On comparison with the above improved value for cetene one finds, however, as the difference:

a value which is in complete agreement with the terminal double bond.

[- 2 HI = 126.59 - 126.92 = - 0.33

[- 2 HI = 126.40 - 126.92 = - 0.52,

U t r e c h t, Pharmaceutical Laboratory of the University.

(Received January 13th 1938).