A C T A 11 H I V E R S I T A I I S L 0 0 Z 1 E N S I S FÜLLA CHIMICA 9, 1991
Jó zef K ula*, K rzysztof ś m ig ie ls k i* , Jó zef Góra*
ELECTROCHEMICAL METHOXYLATION OF ISOPULEGOLE (1 ) ANO Of-PINEME ( 2 ) * *
In the course of our in v e s tig a tio n on e le ctro c h e m ical syn th esis the e le ctro c h e m ical m éthoxylation of isop ulegole (_1) and oi-pinene (J2) was c a rr ie d out. In the case of 1_ product obtained was a very complex m ixture w ith 3,4-di- methoxy-p-0(9)-menthene (3 ) as the major component. The méthoxylation of 2 y ie ld s so b re ro l dim ethyl d ie th e r [6,8- -dimethoxy-p-l(2)-methane] (£ ) as the major component. The e le ctro c h e m ical m ethoxylatior? of 3-carene, o<-pinene or limonene g ives in the described co n d itio n s a mixture of se v e ra l compounds d i f f i c u l t to separate in to in d y vid u a l com ponents.
Methoxyl d e r iv a tiv e s of a c y c lic and monocyclic terpene d e riv a tiv e s have an a t t r a c t iv e odour im pression. Examples of these de r iv a t iv e s are 7-methoxyelgenole ( o s i r o l e ) , 7 - m eth o x ycitro n e lla l and menthol methyl ether [ l ] . Their a t t r a c t iv e fla v o u r is also c o n f ir med by our in v e s tig a tio n s on e le ctro c h e m ical sy n th e s is of methoxyl d e r iv a tiv e s of a c y c lic aldehydes and terpene a lc o h o ls [2 ].
In the present paper we aim to show some r e s u lts of our in v e s tig a tio n on the sy n th e sis of methoxyl d e r iv a tiv e s co n tain in g c y c lic (p-methane) carbon sk ele to n . Taking in to account these assumptions and a v a i l a b i l i t y of raw m a te ria ls the e le ctro c h e m ica l m ethuxylation of isop ulegole l_ and a-pinene 2_ was c a rr ie d out. ( F ig . 1).
In s t it u t e of General Food Chem istry, T ech n ical U n iv e rs ity of Lbd i, Poland.
06H3 0CH3 1 3 3 > k r 0CH3 2 F ig . 1
Isop uleg ole 1_ is an e a s ily a v a ila b le compound as i t is an interm ed iate in the syn th esis of 1-menthol'from d - c i t r o n e l l a l .
In our experiments Iso p u le g o le , chemical p u rity 80%, contain in g 20% of neoisopulegole, was used. The process of e le ctro ch e m ical m ethoxylation was c a rrie d out in a ty p ic a l th re e- e lectro d e non-dia phragm c e l l . The re a c tio n took place in methanol excess at a tempe ra tu re clo se to a room temperature (2 8 °C ), the base e le c t r o ly t e was sodium p -toluenosulfonate. A fte r supplying an e l e c t r i c charge of 1 to 5 F/mol, the process was stopped and a f t e r d i s t i l l a t i o n of unreacted methanol the product was ex tracted with ether and sepa rated by gas chromatography. I t was found th at the re a c tio n was complex and in each case the product obtained was a very complex mixture of many compounds. The IR s p e c tra l a n a ly s is of the re a c tio n m ixture showed th at ap art from eth ers also other fu n c tio n a l groups such as ketone, hydroxyl and o le fln e groups were present. The raw product of e le c tro s y n th e s is was d ivid ed in to fr a c tio n s depending on b o ilin g p o in t. The fr a c tio n w ith b o ilin g point of 80 to 110°C/1,0 mm Hg c o n s titu te d 40% of the to t a l and was the most in te r e s tin g one from the perfum ery’ s p u n t of view. I t contained about 70% of the major component. This compound was separated in a pure s ta te by column chromatography (K ie s e lg e l 60; petroleum eth e r/eth er 98 : 2 ), and
i t s s tru c tu re was determined by *H NMR and MS spectra a n a ly s is . The MS spectrum contained a d is t in c t m olecular peak at 198, w hile the NMR spectrum revealed the presence of two methoxyl groups at 5 = 3125 and 3.15 ppm. Other c h a r a c t e r is t ic s ig n a ls were as follow s: a t r i p l e t at 5 * 4.42 (1 H, 0 * 6 H z), a m u ltip le t at 6 = 4.87 (2 H) and a deformed s in g le t at 6 < 1.53 (3 H) and doublet at
6 = 0.85 ppm (3 H, 3 ‘ 7 Hz).
On the b a sis of these data the compound s tru c tu re was proposed as 3,4-dimethoxy-p-8(9)-menthene 2- This s tru c tu re was also con firm ed by IR 3090, 1655 (C=CH2) , 1125, 1100, 1060, 1020 cm* 1 (C-0-C).
The other compound subjected to the e le ctro c h e m ical méthoxyla tio n was ot-pinene 2. ot-pinene is a cheap and e a s ily a v a ila b le terpene hydrocarbon present in abundance, among o th ers, in P o lis h tu rp e n tin e . Due to the presence of a double bond and cyclobutane rin g the component was expected to methoxylate and the re a c tio n product was expected to be a compound (o r a m ixture of s e v e ra l compounds) w ith a preserved pinene skeleton or with an open cyclo- butane rin g , as i t often occurs in man/ other transfo rm atio ns of a -pinene.
The process of e le ctro c h e m ical m éthoxylation was c a rr ie d out in the same co n d itio n s as in the case of iso p u le g o le . The main and almost only re a c tio n product with 62 to 65% y ie ld appeared to be so b re ro le dim ethyl ether (6,8-dim ethoxy-p-l(2)-m enthene) 4. whose s tru c tu re was determined by l H NMR spectrum a n a ly s is .
*H NMR: v in y l proton 5 * 5.31 ppm (1 H, b r .d ) two methoxyl groups 5 s 3.24 and 3.05 ppm (3 H each, s ) , proton at C-6
carbon S * 3.25 ppm/i H, the s ig n a l o verlap s w ith the s in g le t of methoxyl group 3.24 ppm/l-CH^ group 5 ■ 1.63 ppm (3 H, br. s ) , gem methyl groups 5 s 0.98 and 0.96 ppm ( 6 H, two s ) . I t is w orthw ile to mention th at in the NMR spectrum two a d d itio n a l s in g le ts whitch are clo se to the main protons of methoxyl groups are obser
ved
( S *
3.23 and 3.03 ppm). This gives evidence th a t the productis a m ixture of isomers w ith d if fe r e n t C6-0CHj group c o n fig u ra tio n s .
According to gas chromatography the m ixture of these two compounds is in the r a t io 5 : 1. I t should be stre ssed th at e le ctro c h e m ical m éthoxylation of a- p in e n e is a s e le c t iv e process re s u ltin g In a s a t is f a c t o r y y ie ld of sob rero le dim ethyl e th e r. On the other hand,
the attempts of m éthoxylation of the o th er, main component of t u r p e n tin e, 3-carene, in the co nd itio ns described above r e s u lt in a complex re a c tio n which y ie ld s a mixture of s eve ra l compounds d i f f i c u lt to aeperate into in d iv id u a l components. A s im ila r c h a ra c te r has the ele ctro ch em ical m éthoxylation of P-pinene and limonence.
EXPERIMENTAL
Apparatus
T yp ical theree-electro d e e le c tr o ly z e r (volume 0.035 dm^) pro vided with a re flu x condenser.
Cathodes: Platinum 0.2 x 0.2 x 0.02 dm Anode: Platinum 0.2 x 0.2 x 0.02 dm.
The anode is placed c e n t r a lly between the cathodes in a d i stance of 0.3 dm.
E le c t r o ly t e : Sodium p -tolu en esu lfo nate (0 .5 g) in methanol
2 ( 0 . 7 m ol). Current d e n s ity : 5.0 A/dm .
Performance
The s u b s t r a t e (0.025 mol) i s added to the c e l l and the mixture i s e l e c t r o l y s e d a t 28°C u n t i l 3 F/mol has been d i l i v e r e d . The ex cess methanol i s evaporated in vacuo and the product e x t r a c t e d w ith e t h e r . The e x t r a c t i s washed w ith w a te r, d r ie d w ith sodium s u l f a t e ,
and the so lven t evaporated. When isop ulegole 1_ is used, the remain ing is f r a c t io n a lly d i s t i l l e d to c o lle c t fr a c tio n b o ilin g 80- -110°C/1.0 mm Hg, The major component-3,4-dimethoxy-p-8(9)-menthene
2 was is o la te d by column chromatography and i t s s tru c tu re determ in
ed as shown above.
In case of a- p in en e 2 the remaining is f r a c t io n a l ly d i s t i l l e d to give 0.01.6 mol of 6,8-dimethoxy-p-l(2)-menthene A.; b.p .
130--133°C/20 ram Hg; n* 9 = 1.4658; IR ( f i l m ) ; 2960, 2940, 2830, 1650,
REFERENCES
[1] S. A r c t a n d e r , Perfume and F lavo r Chem icals, M o n tc la ir, New York 1969.
[2] 3. G ó r a , K. ś m i g i e l s k i , 3. K u l a , Zesz. Nauk. P t , Techn. Chem. Spoź., 39, 115 (1905).
Jó z ef Kula, K rzysztof Ś m ig ie ls k i, Jó z ef Góra
ELEKTROCHEMICZNE METOKSYLOWANIE IZOPULEGOLU (1 ) I ca-PINENU (2)
Przeprowadzono elektrochem iczne metoksylowanie izopulegolu (X ) i oi-pinenu ( ¿ ) . W przypadku i powstaje mieszanina sk ład ająca s ię z bardzo w ielu związków chemicznych; głównym składnikiem je s t 3 ,4-dimetoksy-p-8( 9)-inenten ( 2 ) . Metoksylowanie 2 prowadzi głównie do d ie te ru dimetylowego sebrerolu [6,B-dim etyoksy-p~l(2)-m enten] (4). Elektrochem iczne metoksylowanie w podanych warunkach 3-karenu, (3- -pinenu i limonenu prowadzi do trudnej do p o d z ie le n ia m ieszaniny, s k ła d a ją c e j s ię z k ilk u związków chemicznych.
