Notes on scientific research. 155 



Methylenecamphor acetic acid. — Methylenecamphor offers in the shape of its chloride 

 an easily available and practical starting material for undertaking synthetical work in the 

 camphor group, especially with the object of producing compounds which show a strong 

 rotation. In this manner Rupe and Iselin 1 ) prepared a series of derivatives of methylene- 

 camphor from methylenecamphor chloride. Subsequently H. Rupe and E. Burckhardt 2 ) 

 attempted to abtain an unsaturated ketone from the same material. They imagined that 

 the reaction of methylenecamphor chloride (I) on sodioacetoacetic acid ester would 

 produce «-(camphorylidene-3-methyl)-acetoacetic acid ester (methylenecamphor-aceto- 

 acetic acid ester) (II) and that one could transform the latter by means of ketone-scission 

 into the ketone (III), namely methyl-(/?-camphorylidene-3-ethyl)-ketone, the one they desired 

 to find. However, the acetoacetic acid ester derivative proved to be very unstable, as 

 when they worked in an alcoholic solution (even to the total exclusion of water), in 

 consequence of an alcoholysis the acid scission took place and the acethyl-radicle was 

 split off as acetic acid ester. When, however, sodioacetoacetic acid ester free from 

 alcohol was employed, the reaction developed in a much more complicated manner. 



•t „ /C:CHC1 . H /C:CH.CH.C0 2 C 2 H 5 ■ ' /CrCH-OVCOCH, 



C8Hl4 \C0 CsHl4 \C0 CO-CHs CsHl4 \C0 



I) methylenecamphorchloride. (II) cc-(camphorylidene-3-methyl)- (III) methyI-(/?-camphorylidene-3-ethyI)-ketone. 

 acetoacetic acid ester (methylene- 

 camphor acetoacetic acid ester). 



/C:CH-CH 2 -CO,H /C:CH-CH 8 -CH:C\ 



C8H,t \co CsHll \co oc/ CsHl1 



(IV) /9-(camphorylidene-3)-propionic acid (V) a,/-^t'-(camphorylidene-3)-propane (fo'smethylene- 

 (methylenecamphor acetic acid). camphormethane). 



9 1 



" - /C(OH)-CH 2 CH 2 -C0 2 H „ „ /C-CH 2 CH 2 CO 



CsH <co CsHl4 \co 



(VI) fi-(lnjdroxy-3-camphoryl-3) propionic acid. (VII) lactone of the /3-(hydroxy-3-camphory\-3) 



propionic acid. 



The easily available main product of the synthesis is the ester of the ^-(camphor- 

 ylidene-5)-propionic acid or methylene camphor acetic acid (boiling point 171 to 172° 

 at 10 mm.); and from this ester the acid itself (IV) can easily be obtained by saponification 

 with hydrochloric acid. Its melting point is at 106°. Ozone reacts with it producing 

 camphorquinone. A by-product of the reaction of methylene camphor chloride on 

 sodium acetoacetic acid ester is the yellow-coloured a,y-&is-(camphorylidene-5)-propane 

 (frismethylene camphormethane) (V), melting at 265 to 267° whereby the carboxethyl- 

 group is split off also. 



Sodium amalgam does not hydrogenize the double bond of the methylenecamphor 

 acetic acid, on the contrary, the ketone group is attacked whereby a hydroxyacid is formed. 



When boiled with caustic alkali solution, methylenecamphor acetic acid forms the 

 salt of the ft-(hydroxy-3-camphory\-3)-prop\omc acid (VI), whereas the free acid, on 

 acidulation immediately turns into its lactone (VII), which melts at 207°. 



The camphor-radicle most energetically holds fast the double bond of the methylene- 

 camphor acetic acid, in the same manner as in the case of the /^/-unsaturated (,^-phenyl- 

 vinyl)-acetic acid, the so-called phenylisocrotonic acid which is the aromatic analogue 

 of methylene camphor acetic acid. 



!) Berl. Berichte 49 (191), 25; Report October 1916, 123. — *) Berl. Berichte 49 (1916), 2547. 



