AROM ATIZATION STUDIES IN THE NAPHTHALENE SERIES A D issertatio n in Chemistry Presented to the Faculty of the Graduate School of the U niversity of Pennsylvania in P a rtia l Fulfillm ent of the Requirements fo r the Degree of Doctor of Philosophy uperviefor Chairman of Group Committee A rthur Irwin Lowell P hiladelphia, Pennsylvania 1951 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGEMENT This in v estig atio n was undertaken at the suggestion of Dr. E. C. Horning. The author wishes to take th is opportunity to express his thanks to Dr. Horning fo r h is valuable advice and assistance during the course of th is work. Fellowships from the Research Corporation and B risto l Laboratories are g ra te fu lly acknowledged. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS Page Introduction . . . . .................................................................... 1 Discussion: Dehydrogenation ............................................... 3 D iscussion of Experimental .................................................... 15 Discussion: Spectra .......................................... ..................... 53 E x p erim en tal........................................................................................64 S u m m ary .........................................................................................................115 B ib lio g ra p h y ..............................................................................................116 B io g r a p h y .................................................................................. 120 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Introduction During the past th irty years numerous examples of the dehydrogenation of an a lic y c llc compound to an aromatic compound have been reported. Many types of a lic y c llc compounds undergo dehydrogenation under the appropriate conditions, and th is general method has been used as a route to many arom atic compounds. I ts chief use has been fo r stru c tu ral purposes, i. e. to elucid ate the stru ctu re of n atu rally occurring compounds. W ithin the past few years i t has come into Increasing use as a p reparative method to synthesize compounds in th e ir own rig h t or as a supplement to i t s use in stru c tu ra l determ inations. The work to be described in th is d iss e rta tio n concerns the synthesis of certain su b stitu ted 3,4-dihydro- naphthalenes and th e ir conversion to the re la te d naphthalenes by c a ta ly tic dehydrogenation. A series of 1,2,3,4-tetrahydronaphthaleneo were also prepared by the reduction of the corresponding 3,4-dihydro- naphthalenes. Since several series of compounds were prepared vary­ ing in type, number and location of su b stitu e n ts, and degree of satu ratio n , the opportunity to study the effect of these facto rs on the absorption of u ltra v io le t lig h t was taken. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 The synthesis of several new 1-naphthols through arom atlzation of the appropriately su b stitu ted 1-te tra lo n e s was also attempted. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 Discussion: Dehydrogenation The conversion of an a lic y c llc compound at the same formal lev el of satu ratio n as an aromatic compound, or a t a higher lev el, to an aromatic compound Is called arom atizatlon. A d e fin itio n of "aromatic character" Is based upon th e number of p ro p erties which are common to arom atic stru ctu res and whose possession gives the molecule th is q u ality . These pro p erties may be used to define "aromat- ic ity " , or they may be regarded as the m anifestations of the nature of a stru ctu re which involves a ring system of the benzene type. Of these p ro perties one of the most fundamental is the unusual s ta b ility of the ring system as compared with the s ta b ility in the lig h t of a lic y c llc considerations. Thus benzene has le ss tendency to decompose than the hypothetical a lic y c llc cyclohexatriene with non- in te ra c tin g double bonds. This unusual Im m utability is re fle c te d q u a lita tiv e ly in the thermal data fo r the com­ bustion and hydrogenation of benzene and fo r the dehydro­ genation of dihydrobenzene (when compared with the calculated "alicy cllc" values). There are numerous methods which can be used to convert a lic y c llc compounds to aromatic compounds. They are de­ pendent upon the stru ctu re of the a lic y c llc precursor. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 Isom erization has been used to effect the conversion of a lic y c llc stru ctu res to th e ir aromatic Isomers. This method 1b dependent upon the re la tiv e s ta b ility of the two forms, and on the ease of tra n sitio n from one form to the other. The aromatic form is usually more stab le. The ease of tra n sitio n from one form to another u su ally d eter­ mines the p o s s ib ility of separate existence of the a lic y c llc molecule, esp ecially if the aromatic molecule is more stab le. In some cases where an a lic y c llc compound is the intended product, i t s aromatic Isomer Is obtained; the conditions of the reaction induce isom erization. In other cases the a lic y c llc compounds do have a separate existence and isom eric arom atizatlon only awaits su itab le conditions. A licycllc-arom atic isom erization u su ally can occur through two general methods: (l) carbon-to-carbon fissio n and (2 ) hydrogen re d istrib u tio n . Carbon-to-carbon fissio n usually occurs in the tran s­ form ation of stru ctu res with bridged rings to the arom atic Isomer, and ring contraction and isom erization in other cases, to mention a few examples. An a lic y c llc compound can d iffe r from i t s arom atic Isomer in the arrangement of hydrogen atoms alone. Isomer­ iz a tio n In these cases requires only the re d istrib u tio n of the hydrogen atoms so that the ring or rin g s acquire, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 through th is process, an amount of unsaturation correspond- I ing to the Kekule type of stru ctu re. Acids and bases, hydrogenation c a ta ly sts, dehydrohalogenatlon, and heat have been used to effect Isom erization of a lic y c llc compounds. Dehydrogenation is another method which can be used to convert an a lic y c llc compound to an aromatic compound. The work described In th is d isse rta tio n concerns an in­ v estig atio n of the synthesis of certain a lic y c llc com­ pounds and th e ir conversion to arom atic compounds by the removal of hydrogen. During the past three decades, dehydrogenation has been used mainly fo r stru c tu ra l studies of organic n atu ral products. Notable early examples of i t s use in elu cidating stru ctu re are in the polyterpene researches of Ruzicka (l) and the dehydrogenation of cho lestero l and cholic acid which played an Important part in determ ining the stru ctu re of the ste ro ls (2). Haworth and Richardson (3), In th e ir in v estig atio n s concerning the stru ctu re of podophyllotoxln, converted podophyllotoxln into a compound containing the 1-phenylnaphthalene nucleus (I). They also prepared I by an unambiguous method through dehydrogenation of the lactone II. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 OcH, OCH3 CH30 Or^^irOCi IS O M . v o ------------> CHxOH popopHyuuoroxiM P K R O P o p o PHYUIN I pd-black ocH3 OCH, ch^o^ \ , oc^ 3 pp- oO QLftCK X DEH YD RO P N H Y D R O - P lcR O P o D O P H Y L L lU The use of ordinary degradatlve methods to esta b lish the stru ctu re of high m olecular weight a lic y c llc compounds is d if f ic u lt and time consuming in many cases. The con­ version of these compounds into re la te d arom atic compounds by dehydrogenation answers the question of ring size and p o sitio n , and p o sitio n of su b stitu en ts. Dehydrogenatlon has come into increasing prominence during the past few years as, a synthetic route to arom atic compounds. This method is useful in many cases in stru c­ tu ra l work, since the product of an unambiguous syn thetic procedure may be compared with that obtained from a degradatlve procedure. Bergmann and coworkers (4) synthe­ sized arom atic reference compounds by dehydrogenatlon during Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 th e ir in v estig atio n into the mechanism of the Wagner- Jauregg reaction. There are three reagents in preferred use at the present time, su lfu r, selenium, and the platinum m etals. The importance of su lfur in dehydrogenatlon was f i r s t recognized “by Ruzlcka (1). Selenium was introduced by D iels (5). Platinum and palladium in various forms are also used. The use of palladium deposited on fin e ly divided carbon is finding increasing favor. Not very much is known about the reaction mechanism of dehydrogenatlon. Any study of the mechanism of dehydro­ genation with the several reagents used w ill have to concern i t s e l f with accompanying thermal effe c ts since dehydrogenations are usually carried out at re la tiv e ly high tem peratures. The platinum metals are used as hydro­ genation cataly sts; they have the a b ility to tra n sfe r hydrogen from one organic molecule to another, or simply to add and/or remove hydrogen from certain stru ctu res, with or without the aid of m olecular hydrogen. This property has been u tiliz e d for dehydrogenatlon purposes. Selenium and su lfu r act on the a lic y c llc molecule in a way th at the hydrogen is elim inated as hydrogen selenlde or hydrogen su lfid e, as the case may be. Selenium has been reported to have very slig h t a c tiv ity as a hydrogenation c ata ly st, but according to P la ttn e r (6 ), c a ta ly tic dehydrogenations are probably based on fundam entally d ifferen t reactio n s Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.