US3390192A - Dihydropyrenes and photochromic compositions based thereon - Google Patents

Description

United States Patent O 3,390,192 DIHYDROPYRENES AND PHOTOCI-IROMIC COMPOSITIONS BASED THEREON Luther A. R. Hall, Woodclilf Lake, N.J., and John A.

Gurney, Tarrytown, N.Y., assignors to Geig'y Chemical Corporation, Greenburgh, N.Y., a corporation of Delaware No Drawing. Filed Oct. 20, 1965, Ser. No. 499,037 Claims. (Cl. 260-666) ABSTRACT OF THE DISCLOSURE 15,16-methylene-l5,16-dihydropyrenes and polyalkyl- 15,16-dimethyl-l5,16-dihydropyrenes having photochromic properties are prepared via multistep ring closure of bisphenolic compounds to yield metacyclophanes which 'are then subjected to several steps of oxidation, reduction and dehydrogenation. Typical embodiments are 15,16 methylene l,3,6,8 tetramethyl 15,16 dihydropyrene and 1,3,6,8,15,16-hexamethyl-15,16-dihydropyrene.

Detailed description This invention relates to organic compounds reversibly convertible from colored to colorless isomeric forms. More particularly, it relates to 15,16-dihydropyrenes, which are photochromic, that is, when exposed to light the compounds become colored or colorless, depending on their structure, and, when put in the dark, they revert to their original state. These valuable compounds find application as self-attenuating light valves in articles such as tinted safety glass and headlights for automobiles; infrared screens, solarium windows, display windows and automatic curtains; in information retrieval apparatus such as computer memory core devices; toys; photocopying devices, light meters, and the like.

The compounds contemplated by the instant invention are those of the formulae:

wherein:

R and R are hydrogen, alkyl, cycloalkyl, aryl or CH Z, with the proviso that R; includes hydrogen only if R is other than hydrogen;

R is alkyl, aryl or CH Z;

R is (CH n being from 1 to 18, CR=CR or o-arylene; and

Z is chloro, bromo, cyano, carboxamido, carboxyl, or

carboalkoxyl.

ice

By the term alkyl and derivations thereof such as alkoxy are meant branched or straight chained saturated hydrocarbon groups of from one to about thirty carbon atoms. Representative of such groups are thus methyl, ethyl, propyl, isopropyl, butyl, s-butyl, t-butyl, pentyl, hexyl, octyl, decyl dodecyl, tetradecyl, hexadecyl, octadecyl, eicosyl, decosyl,- tetracosyl, hexacosyl, octacosyl, triacontyl and the like. When the term alkyl is qualified by the designation lower, there is included branched or straight chain hydrocarbon groups of from one to about six carbon atoms.

In certain formulae, the substituents in the 15,16-positions are attached through dashed and solid lines. This conventionally indicates position isomers, dashed lines being downwardly directed, solid lines being upwardly directed to show clearly the trans forms.

Special mention is made of an important embodiment of the instant invention. This comprises compounds of the formula:

wherein R is as hereinabove defined.

Among the valuable members represented by this formula is mentioned l,3,6,8,l5,16-hexamethyl-l5,l6-dihydropyrene (R is CH which is photochromic per se, and which serves as a valuable intermediate for photochromes with a variety of functional groups.

Still another embodiment of this invention is represented by the formula:

wherein R and R are 'as above defined. Illustrative of a particularly important species of this embodiment is 15,16 methylene l,3,6,8 tetramethyl 15,16 dihydropyrene (R is CH and R is CH which is a valuable photochrome per se, and which serves as an intermediate to prepare compounds of the above formulae bearing a wide variety of substituents.

Still a further embodiment of this invention is a photochromic composition comprising a dihydropy-rene of the formulae above and an inert carrier. Illustrative of such inert carriers are synthetic organic polymeric substances, such as poly(vinyl chloride) resins.

A further embodiment of this invention is, in essence, a method for imparting photochromic properties to a substrate which comprises incorporating in said substrate an elfective amount of a dihydropyrene as defined above. Illustrative of said substrates is poly(vinyl chloride).

The 15,16-disubstituted-15,16-dihydropyrenes of this invention can be prepared in a variety of ways. One especially convenient synthetic pathway is outlined as follows:

R1 orrmsot R1 NaOH wherein R and R are as above defined. This sequence,

which will be fully exemplified in detail, generally combr 0 prises treating a readily available or easily prepared trisubstituted phenol with a methylating agent, such as dimethyl sulfate, followed by introduction of chloromethyl groups into the remaining unsubstituted positions. (Of course, if it is desired that the ultimate product contain substituents other than hydrogen at the 4, 5, 9 or 10 positions, it is convenient to introduce them at this step by using, for example, aldehydes other than formaldehyde, such as butyraldehyde or benzaldehyde.) Next, the chlotime in the 3 and s-positions is replaced with iodine by a reaction in which the chloroalkyl compound is treated with an iodide, such as sodium iodide. This provides a diiodo compound which is treated then with a coupling reagent such as sodium and tetraphenylethylene until the formation of a cyclized derivative is substantially complete. Next, the methoxyl groups are oxidized to quinone functional groups with ferric chloride, and the tri-cyclic ring system is converted to the tetra-cyclic ring system. Further oxidation is carried out with oxygen and base. The keto groups are reduced to methylene groups with lithium aluminum hydride and aluminum chloride and the desired 15.16 disubstituted 15,16 dihydropyrene is obtained by dehydrogenation over a palladium catalyst.

ttd m The 15,16-bridged compounds of this invention represented by the formula wherein R and R are as above defined can be prepared by a number of techniques. Especially convenient is the synthetic pathway outlined as follows:

R R 11+ Meso. +HCHO on,

I NaOH HQ}! on OMe ClCH

CHsCl OMB BUR

HCHO/HCI I ZnOlz/LiCl (1) MeMgI (2) FeCla (.)Mo ()Me R R nflqz ClCH HCHOIHCI I iMeMgI H: OH, I ZnCIz/LiGl I ClCH R -R R R OMe 0M1;

OMe 0 I I R R R R F8013 O1 CH2 C 2 K NaOH R i R R R OMe (L 1 LiAlHt l AlCl; (2) Pd/C wherein R is as hereinabove defined and Me means methyl. Of course, as will be obvious, compounds of this invention bearing R groups defined hereinabove, in the 4, 5, 9 and 10 positions can be prepared by haloalkylating the dimethoxydiphenylmethane with an appropriate aldehyde instead of formaldehyde. The above sequence will be exemplified in detail later; it comprises treating a 2,6- disubstituted-phenol with formaldehyde and an acid to form a bis-phenol derivative, which is converted to a dimethoxy derivative with dimethyl sulfate. One aromatic hydrogen atom in each ring is next replaced with a haloalkyl group, and methyl magnesium iodide and ferric chloride are used to form the tricyclic ring system. This compound is bis(chloromethylated) and the tetracyclic ring system is formed in the presence of methyl magnesium iodide. This is converted to its quinone derivative with ferric chloride, then oxidized, reduced and dehydrogenated in a manner completely analogous to that used to prepare the corresponding 15,16-disubstituted 15,16- dihydropyrene described above.

The preparation of compounds wherein R is m being from 2 to 18, is accomplished by forming a his phenolic compound in which the phenol radicals are joined para to para through a methylene bridge of appropriate length, then using this as a starting material in the sequence outlined above. The corresponding o-arylene compounds are obtained if the bis phenolic starting material is joined para to para through adjacent carbon atoms in an aromatic ring.

The following examples are given solely for the purpose of illustration and are not to be construed as limitations of this invention, many variations of which are possible without departing from the spirit or scope thereof.

Example I.1,3,6,8,l5,16-hexamethyl-l5,16- dihydropyrene (a) Methoxymesitylene.-2,4,6 trimethylphenol, 29.5 g., 0.217 mol, prepared by the procedure of Hart and Buehler, J. Org. Chem., 29, 2397 (1964), sodium hydroxide, 12.6 g., 0.316 mol, dissolved in 126 ml. of water, and 19.7 ml. of dimethyl sulfate, 0.217 mol, are mixed in a vessel cooled in an ice bath. The temperature is raised and maintained at 50:1 C. for one hour, then 7.50 g. of sodium hydroxide in an equal weight of water and 10 ml. (0.100 mol) of dimethyl sulfate are added at 3 hour intervals during 15 hours. The product is isolated by extraction of the aqueous reaction mixture with seven -ml. portions of ether. After washing the ether layer with 25% sodium hydroxide and evaporating the ether, the residue is fractionally distilled and 26.9 g. of methoxymesitylene, B.P. 29 C./0.4-0.45 mm, 83% yield, is obtained.

(b) bis(chloromethyl)methoxymesitylene. A mixture of methoxymesitylene, 7.4 g., 0.049 mol, paraformaldehyde, 7.82 g., 0.197 mol, lithium chloride, 9.82 g., 0.245 mol, and zinc chloride, 4.80 g., 0.049 mol, is heated to C. and anhydrous hydrogen chloride is passed in. Addition of gas is continued for 5 /2 hours at 72i2 C. during which time monochloromethylated product, which appears first, is converted to the desired bis chloromethylated product. The reaction mixture then is poured into ml. of ice, and the solid material is collected on a filter and washed with water. There are obtained 11.5 g. of bis(chloromethyl)methoxy mesitylene, 94% of theory. Recrystallization from ethyl acetate yields 9.05 g., M.P. -136 C.

(c) Bis(iodomethyl)methoxymesitylene. Bis(chloromethyl)methoxymesitylene, 8.0 g., 0.0324 mol, sodium iodide, 40 g., 0.26 mol, and 400 m1. of tetrahydrofuran are refluxed for 6 hours. The reaction solvent is removed by distillation at 15 mm. pressure. Methylenechloride, 100 ml., and 300 ml. of ice water are added. The aqueous phase, after separation of methylene chloride is extracted 4 times with 20 ml. of methylene chloride. The combined organic layers are percolated through 200 ml. of crushed calcium sulfate then treated with decolorizing charcoal. The methylene chloride filtrate is concentrated in a vacuum to 30 ml. volume and 55 ml. of methanol are 7 added. The precipitate is collected and recrystallized first from toluene, and then from ethyl acetate to yield 9.62 g. of bis(iodomethyl)methoxymesitylene, M.P. l34138 C., 69% yield.

(d) 6,8,14,16,4,12 hexamethyl-7,l dimethoxy(2,2)- metacyclophane. Bis(iodomethyl)methoxymesitylene, g. in 50 ml. of dry tetrahydrofuran (THF) is added at 1 drop per second to sodium sand, g., 0.87 mol, suspended in 1 liter of refluxing THF and 2 g. of tetraphenylethylene. The system is stirred under nitrogen with a Vibromixed stirrer. Unreacted sodium is filtered off and the THF is removed by distillation in such a way that the pot temperature remains at or below C. The residual solid is dissolved in 250 ml. of methylene chloride. The solution is percolated through 15 g. of Florisil, then the methylene chloride is evaporated off leaving a residue, which is dissolved in ml. of hot carbon tetrachloride. The solid which precipitates on cooling is collected and treated with 30 ml. of hot cyclohexane. The cyclohexane solution is cooled and the desired product precipitates. There are obtained 11.7 g. of crude material which are chromatographed on alkaline alumina. After rcchromatographing, there is obtained 0.73 g. of material, M.P. 220-213 C.

(e) Bis dienone.The product of Step (d) is treated with ferric chloride. A solution of 1.00 g. of the methacyclophane in 100 ml. of dry chloroform is stirred at room temperature for three hours with 3.5 g. ferric chloride. A precipitate of a reddish-brown inorganic complex of the bisdienone is formed and this is collected by filtration. This solid is immediately suspended in 100 ml. chloroform and 20 ml. 3 N hydrochloric acid. This suspension is shaken until solution occurs; the chloroform layer is separated, washed with water and concentrated. The reddish brown solid, about 1.2 g., is treated with charcoal in boiling ethanol, filtered, and the ethanolic solution is concentrated to about 20 ml. From the cold solution separates 0.9-1.0 g. of a yellow solid.

(f) Quinone.The prod-uct of Step (e) is treated with oxygen in the presence of sodium hydroxide. A suspension of the bisdienone (190 mg.) in a solution of methanol ml.), water (15 ml.), and sodium hydroxide (2.5 g.) is stirred for 12 hours at room temperature. The resulting solution is concentrated under reduced pressure, diluted with water (50 ml.), and extracted with 20 ml. methylene chloride. The blue aqueous layer is extracted again with solvent, and the combined organic extracts are dried and concentrated. The residue is sublimed at ISO-200 (0.1 mm.). The orange sublimate is dissolved in chloroform, diluted with petroleum ether, and after standing overnight at l0 the resulting crystalline product (175 mg., 90%) is collected.

(g) Hexaene-The product of Step (1) is treated with lithium aluminum hydride and aluminum chloride. To a solution of 7 g. of aluminum chloride in 120 ml. of ether, 2 g. of powdered lithium aluminum hydride is added with stirring, and the suspension is boiled under reflux for 2 hours. After cooling, a 90 ml. portion of the clear supernatant is withdrawn, transferred to a reaction flask and cooled to 80.

The quinone of Step (f) (300 mg.) in 10 ml. benzene is added to 200 ml. of ether and the suspension added dropwise with stirring to the mixed reducing agent at -80 C. over a 2 hour period. The suspension is slowly warmed to room temperature and boiled for 0.5 hour. After destroying the excess reagent with ethyl acetate followed by water, and separation of the ether layer, evaporation under reduced pressure yields a green residue which is unstable to light and air.

(h) Dihydropyrene.-The product of Step (g) is treated with palladium and dehydrogenated. A suspension of 50 mg. of 5% palladium-charcoal in 25 ml. of benzene containing 1 ml. of acetone is refluxed for 15 minutes. To this mixture is added 50 mg. of the above green solid and hcatnig is continued for 6 hours. The suspension is cooled,

G. Geon l03-EP resin 100.0 Advastate T3 stabilizer 2.0 Stearic acid 0.5

l,3,6,8,15,16-hexamethyl-l5,16-dihydropy1'ene 0.005

The dihydropyrene is solvent blended (methylene chloride) with the powdered poly-vinyl chloride) and other additives and the solvent is evaporated. The batch is milled on a two-roll plastics mill for 5 minutes at 350 C. The milled sheet is compression molded at 365 F. into four 5 x 5 x 0.045 inch sheets in a picture frame mold. (Molding cycle: 5 min. at contact pressure; 45 sec. at 5 tons, 45 sec. at 10 tons, 45 sec. at 15 tons, 45 sec. at 20 tons, then flash quench in cold water.) The colored plastic films clear on exposure to light and returns to a colored form when left in the dark.

Example lI.-15,16-methylene-1,3,6,8-tetramethyl- 15,16-dihydropyrene (a) 4.4'-methylene bis(2,6-xylenol).-The reaction of 2,6-xylenol (122 g., 1.0 mol in 120 ml. of absolute ethan01), trioxane (18 g., 0.6 formaldehyde eq. in 170 ml. absolute ethanol) conc. hydrochloric acid (120 ml., 1.32 mols) atfords the bis-xylenol in good yield. The trioxane solution is added over 2.75 hours to a reaction mixture kept under nitrogen at 50-* 1 C. The white product is collected after the reaction mixture has been cooled to -60 C. Washing of the reaction product with a minimum of cold absolute ethanol and drying of the washed product .aifords 101.1 g., yield, M.P. 172.5-177 C. Recrystallization from a 30:70 mixture of ethyl acetate-heptane provides 92.0 g., 72% yield, of long needles, M.P. 175- 178 C.

(b) 4,4'-methylene bis(2,6-dimethylanisole).-Dimethyl sulfate 89 g., 0.705 eq.) is added dropwise during 1 hour to 4,4-methylene bis (2,6-xylenol) (90.0 g., 0.705 eq., M.P. 175-178) which has been dissolved in aq. sodium hydroxide (42.4 g., 1.06 mols, in 425 ml. of water). Thereafter, smaller quantities of sodium hydroxide (21.2 g., 0.53 mol) in one portion and dimethyl sulfate (46 g., 0.35 mol) are added dropwise to the reaction mixture (50i5 C.) at hourly intervals. This treatment is repeated for seven hours. The reaction is completed by adding more sodium hydroxide (21.2 g., 0.53 mol), by slowly dropping in a final charge of dimethyl sulfate (89 g., 0.705 eq.) and by refluxing for an additional 1.5 hours. After cooling to room temperature the solid is collected and dissolved in a mixture of ethyl ether (400 m1.) and water (400 ml.). The ether extract is washed with 25% sodium hydroxide (2X 25 ml.) and with saturated sodium chloride (2x 25 ml.), then dried overnight. Removal of solvent by distillation aflords 75 g., 75% yield, 136-145 "l 0.10 mm., M.P. 78-82.

(0) 4,4 methylene bis(3-chloromethyl-Z,6-dimethylanisole).-Hydrogen chloride is bubbled into a stirred mixture of trioxane (16.9 g., 0.564 mol), lithium chloride (19.2 g., 0.141 mol) and glacial acetic acid ml.). After ten minutes (exotherm 25 to 38 C.) the reaction mixture becomes clear and homogenous. 4,4'-methylenebis(2,6-dimethylanisole) is then added in one portion (10.0 g., 0.0347 mol). The reaction proceeds rapidly /z hour) on a steam bath (pot 80-87 C.). The white product is isolated by mixing the reaction slurry with ice (200 ml.), by washing the filtered solid (M.P. 131-133 C.), which has been dissolved in chloroform, with 10% sodium bicarbonate solution until neutral and by evaporating off the dried solvent. Recrystallization from ethyl acetate (14) affords 19.7 g., 73% yield, M.P. 135-137 C. NMR shows the presence of only one sharp methoxy 9 singlet (3.69 6, p.p.m.) indicating chloromethyl groups at the 3,3 positions.

(d) 4,4 methylene 3,3 (1,2-ethylene) bis(2,6- dimethylanisole.Compound of Step (c) (19.0 g., 0.105 eq. in 1 l. absolute ether) is condensed to the abovenamed product on addition to methyl magnesium iodide (methyl iodide 14.9 g., 0.105 mol; magnesium, 2.50 g., 0.103 mol; 300 ml. abs. ether). The bis chloromethyl compound is added under prepurified nitrogen over a period of 18 hours. The condensed product is obtained by chromatography on alumina. Elution with pet. ether affords 6.3 g., 55% yield, of white powder.

(e) 4,4 methylene 3,3 (1,2 ethylene) bis[5,5'- bis (chloromethyl -2,6-dimethylanisole] .Anhydrous hydrogen chloride is bubbled into a mixture of trioxane (2.4 g.) zinc chloride (2.7 g), lithium chloride (1.7 g.) and glacial acetic acid ml.) to give a homogeneous solution to bis-chloromethyl ether. The double bridged compound is added in one portion (3.1 g.) and the temperature kept at 50:1" C. for 8 hours. The product is isolated by pouring the reaction mixture into ice ml.) and extracting with methylene chloride. The extracts, washed with 2X 10 ml. of 10% sodium bicarbonate, 2X 5 ml. saturated sodium chloride solution, are dried overnight. Recrystallization from toluene affords 3.0 g., 74% yield, of white plates.

(f) 4,12-methylene metacyclophane.The compound of Step (e) (1.0 g.) reacts with zinc dust (0.177 g.), sodium carbonate (0.260 g.) and a catalytic amount of sodium iodide to give the 4,12-methylene metacyclophane. The hot reaction mixture is poured into ice (100 g.) and is extracted with methylene chloride. The extract is washed with water. After the solvent is stripped off, steam distillation provides about an 80% yield of white needles.

g) Bis dienone-The metacyclophane of Step (f) (0.66 g.) and anhydrous ferric chloride (2.0 g., 1.2 mol) dissolved in anhydrous chloroform (80 ml.) are stirred at room temperature for 6 hours to give an insoluble reddish brown complex. The complex is collected by filtration and is decomposed by vigorously shaking with a mixture of chloroform (70 ml.), dilute hydrochloric acid (3 N, 15 ml.) until solution is complete. The separate chloroform layer is concentrated and the red-brown solid is dissolved in 70 ml. of hot ethanol. The hot solution is treated with charcoal and is concentrated to 15 ml. On cooling yellow needles are deposited in about 90% yield.

(h) Quinone.A suspension of the compound of Step (g) (0.50 g., 163 mol) and a water-methanol (70 ml., 150 ml.) solution of sodium hydroxide (10 g., 0.25 mol.) are stirred for 18 hours at room temperature. The resulting solution is concentrated under a water pump, diluted with water (200 ml.) and extracted with methylene chloride (90 ml.). The aqueous layer is extracted further with 225 ml. portions of solvent and all extracts were combined, washed with water, evaporated under a water pump and sublimed (100 C./0.01 mm.) to give a violet solid. Recrystallization from chloroformcyclohexane affords orange needles in about 90% yield.

(i) 15,16 methylene 1,3,6,8 tetramethyl 15,16 dihydropyrene.A reducing solution is prepared by adding lithium aluminum hydride (2.0 g.) to an ether (120 ml.) solution of aluminum chloride (7.0 g.) stirring and refiuxing the mixture for 2 hours and then transferring 80 ml. of cooled supernatant liquid to a preassembled and dried reaction set-up. Dropwise addition of quinone of Step (h) (0.340 g. dissolved in 10 ml. benzene and diluted to 200 ml. with dry ether) to the reducing solution mentioned above at 80 over 2 hours, time yields a mixture of the desired product and a dihydro product. The suspension is warmed to room temperature (1 hour) and then refluxed for /2 hour. The excess reducing agent is decomposed with ethyl acetate and enough water ml.) is added to give two phases. The separated ether phase is dried under vacuum. The resulting blue solid is then refluxed in cyclohexane (200 ml.) with palladium on r 10 charcoal (0.300 g.) for 18 hours to complete dehydrogenation of the dihydro product. After filtration and removal of the reaction solvent the blue solid is sublimed 0.02 mm.) to yield the product in about 60% yield. The following list sets forth some of the compounds Within the scope of this invention prepared by the procedures of the foregoing examples and disclosure. The list is given to avoid unnecessary repetition of experimental details:

15, 16-(1,18-octadecylene)-1,3,6,8-tetramethyl-15,16-

dihydropyrene 15, 16-( 1,2-phenylene) -1,3,6,8-tetramethyl-15,16-

dihydropyrene 15, 16-methylene-15,l 6-dihydropyrene 1,3,4,5,6,8,9,10,15,16-decamethyl-15,16-dihydropyrene 1,3,6,8-tetracyclopropyl-15,16-dimethyl-15, 16-dihydropyrene 1,3,6,8-tetraphenyl-15,16-dimethyl-15,16-dihydropyrene 4,5,9,10-tetraphenyl-15,l6-dimethyl-15,16-dihydropyrene 1,3 ,6,8-tetra(chloromethyl) -15-l6-dimethyl-15,16-dihydropyrene 1,3,6,8-tetra(bromomethyl) -15,16-methylene-15,l6-dihydropyrene 1,3,6,8-tetra(cyanomethyl)-15,16-dimethyl-15,l6-dihydropyrene 1,3 ,6,8-tetra(carbamylmethyl) -15,16-dimethyl-l5,16-

dihydropyrene 1,3 ,6,8-tetra(carboxymethyl)-15,16-dimethyl-l5,16-dihydropyrene 1,3 ,6,8-tetra(carboethoxymethyl) -15,16-dimethyl-15,16-

dihydropyrene 1,3 ,6,8-tetramethyl-15,16-( 1',2-dimethylethylene) -15,16-

dihydropyrene 1,3 ,6,8-tetramethyl-15,16-diphenyl-15,16-dihydropyrene 1,3 ,6,8-tetramethyl-15,16-di(chloromethyl)-15,16-dihydropyrene 1,3,6,8-tetramethyl-15,16-di(cyanomethyl)-15,16-dihydropyrene 1,3 ,6,8-tetramethyl-15,16-di(carboxymethyl)-15,16-

dihydropyrene lower alkyl lower alkyl on. CH3

| I lower alkyl L/ lower alkyl 4. A compound of the formula:

wherein R is hydrogen or lower alkyl.

5. 15,16-methylene-15,16-dihydropyrene.

(References on following page) 11 12 References Cited W. 5. Lindsay et al.: J. Amer. Chem. Soc., 83, pp. UNITED STATES PATENTS 1 2508295 5/1950 Rechmeyer H. R. Blattman et aL: J. Amer. Chem. Soc., 87-(1), 3,231,584 11/1960 Berman et a1. :52 300 1304. 1965- 3,278,449 11/1966 Hardwich et a1. 252300 a V. Boekelheide et aI.: J. Amer. Chem. Soc., 85, 1545- OTHER REFERENCES 1963' 5 ct Bull Chem" Belgian IDELBERT E. GANTZ, Primary Examiner.

Monique De Clercq et al.: Bull. Soc. Chem, Belgian 110 V, OKEEFE, Assistant Examiner. 64, pp. 367-385, 1955.