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One-Stage Synthesis of Hexamethyl-Dewar-Benzene from 2-Butyne.

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after removal of the ether is vacuum-distilled, yielding the
(+)-bromide (2) as a colorless, optically stable liquid, b.p.
23-24"C/0.1 mm, ng = 1.5235, in 53 % yield.
A similar reaction in boiling ether (6.5 hr) gives a 50 % yield
of a (+)-bromide with [a]g3 = +135.3 [*I.
For determination of its optical purity and relative configuration the (+)-bromide (2), [a]&3 = +140.4', was hydrolysed by 2.85 N KOH in dioxane-water (4:7 v/v) at "C to
the (+)-thiophosphonic acid ( I ) , [=I23 = +13.0° (yield 80 %
in 21/2 hr).
C2H50\#Br
C2H< ' S
-
(2). [o]: = + 140.4O
(i), [a]26j= + 13.0°
Comparison of the rotation of the acid obtained by alkaline
hydrolysis with that of the starting material showed that the
(+)-bromide (2) had a n optical purity of at least 94 %. If we
assume that the alkaline hydrolysis occurs with inversion 131
then the thiophosphonic acid ( I ) reacts with (C&)3PBr2
also with inversion. It is remarkable that the reactions of the
acid ( I ) with PC15 and (CaH5)3PBr2 occur in stereochemically identical ways.
Received: May 18th, 1966
[Z 242 IE]
German version: Angew. Chem. 78, 716 (1966)
[*] Rotations were measured for the neat liquids.
[ I ] J . Michalski and M . MikoEajczyk, Chem. and Ind. 1964, 661 ;
Chem. Commun. 1965, 35; Tetrahedron, in press.
[2] L. Horner. H . Oediger, and H . Hoffmann,Liebigs Ann. Chem.
626, 26 (1959).
[3] M . Green and R . F. Hudson, J. chem. S O C . (London) 1963
3883 ; J . Michalski, M . Mikolajczyk, and J. Ondariczuk, Tetra.
hedron Letters 1965, 1779 ; M . Mikolajczyk, Tetrahedron, in
press.
One-Stage Synthesis of
Hexamethyl-Dewar-Benzene from 2-Butyne 111
By Dr. Wolfgang Schafer
Forschungslaboratorien, Chemische Werke Hiils AG.,
Marl (Germany)
Hexamethylbicyclo [2.2.0]hexa-2,5-diene (hexamethyl-Dewarbenzene) (3) can be prepared by trimerization of 2-butyne
( I ) with anhydrous aluminum chloride as catalyst at 20 to
35 "C. Benzene may be used as solvent. Compound (3) was
not previously known [21.
The trimerization of 2-butyne ( I ) may occur by way of a
complex (2) of AlC13 with the tetramethylcyclobutadiene,
which does not exist in the free form.
If 2-butyne ( I ) is trimerized above 50°C the benzene derivative (4) is formed predominantly and only a small
amount of the bicyclic compound (3) can be isolated. Trimerization in boiling benzene gives hexamethylbenzene (4)
in 80 to 9 0 % yield, and a mixture of oils. Some of these
oils are dimerization products of tetramethylcyclobutadiene
previously obtained in a different way [31.
1 kg of 2-butyner41 is dropped, with stirring, during 2.5 hr
into a suspension of 50 g of freshly sublimed AlC15 in 1 I of
benzene (dried over sodium), care being taken, by watercooling, that the temperature does not exceed 35°C. For
completion of the reaction the mixture is stirred for a further
4 hr at 35 "C. (At 20 O C the reaction time is approximately
20 hr.) Then the mixture is cooled to O°C and the catalyst
is decomposed by adding dropwise 50 to 100 ml of water,
until the initially brown mixture turns pale yellow. Unchanged 2-butyne is removed with some benzene by distillation at room temperature and 200 mm, being collected in
two successive receivers cooled by dry ice/methanol. Fractionation of the condensate allows recovery of cu. 200 g of
2-butyne .
The butyne-free benzene solution is washed with water until
neutral and fractionated in vacuum, yielding a first fraction
of benzene and then 490 to 510 g of a colorless liquid (3),
b.p. 43-45 "C/lS mm, n',"= 1.4479, m.p. 7 "C. After cooling,
the distillation residue affords 150-165 g of hexamethylbenzene. Compound (3) can be kept for months in a refrigerator and for a long time even at room temperature
protected from light.
The NMR spectrum of the bicyclic compound (3) in CCl4
(with tetramethylsilane as internal standard) contains two
singlets at 8.4 and 8.9 T, of relative areas 2: 1. The signal at
8.4 T is assigned to the CH3 groups attached to the doubly
bound C atoms, and that at 8.9 T to the methyl groups
attached to tertiary C atoms. The N M R spectrum of hexamethylbenzene ( 4 ) contains only one signal at 7.85 T.
In the IR spectrum of the bicyclic compound (3) there is a
weak band a t 1680 cm-1 (C=C in strained ring systems),
also bands at 1370 cm-1 (-CH3) and 1060 cm-1 (CHyC=C),
as well as at 1280, 1220, 735, and 660 cm-1.
This synthesis enables a Dewar-benzene derivative to be
prepared on a technical scale for the first time [51.
Received: May ZOth, 1966
[Z 243 IE]
German version: Angew. Chem. 78, 716 (1966)
[ I ] The scope of the reaction and the transformations of ( 3 ) are
being studied.
[2] C . E. Berkoff, R . C . Cookson, J. Hudec, and R. 0. Williams,
Proc. chem. SOC.(London) 1961, 312, merely presumed that
formation of ( 4 ) in 20 yo yield on dehalogenation of 3,4-dichlorotetramethylcyclobutene by activated zinc dust in the presence of
( I ) proceeded by way of ( 3 ) ; see also J . chem. SOC.(London)
1965, 194.
[3] R . Criegee, Angew. Chem. 74, 703 (1962); Angew. Chem.
internat. Edit. I , 519 (1962).
[4] Dried over sodium; according to gas chromatography it
contained 92.7 T, of ( I ) .
[51 2-Butyne is obtained, e.g., a s by-product on dehydrogenation
of butane to 1,3-butadiene by Houdry's procedure.
Synthesis and Formula of Biological and Mineral
Carbonateapatite
By Prof. E. Hayek, Dr. H. Konetschny, and Dr. E. Schnell
Institut fur Anorganische und Analytische Chemie,
Universitat Innsbruck (Austria)
The compound ( 3 ) is quantitatively isomerized to hexamethylbenzene (4 ) in the presence of catalysts at room
temperature (enthalpy of rearrangement: AH = -62.4 & 0.4
kcal/mole).
Angew. Chem. internat. Edit. J Vol. 5 (1966) 1 No. 7
The designation carbonate-apatites is given to minerals
(dahllite, staffelite, kollophane) that are analogous to
apatite Ca5(P04)3(F,OH,CI) in crystal structure but contain
also carbonate. Carbonate-apatites also form the mineral
substance of bones and teeth. All carbonate-apatites contain
calcium phosphate and carbonate (the latter in amounts
669
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synthesis, one, stage, butyne, hexamethyl, dewar, benzenes
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