1,4-Bis(5-P-N-Butoxyphenyloxazol-2-Yl)benzene and the Preparaion Thereof

1. Field of the Invention.

This invention relates to dyes which are useful as lasing materials.

2. Description of the Prior Art.

Those interested in the laser field are interested in materials which will lase. The present invention relates to a dye which will lase. Insofar as is known to the inventor, the dye disclosed herein has never been prepared before.

The dye disclosed herein is 1,4 -bis(5-p-n-butoxyphenyloxazol-2-yl)-benzene. It is prepared by (1) brominating p-n-butoxyacetophenone to form p-n-butoxyphenacyl bromide, (2) reacting p-n-butoxyphenacyl bromide with hexamethylene tetramine to form a quaternary salt, (3) reacting the quaternary salt with hydrochloric acid to form p-n-butoxyphenacylammonium chloride, (4) reacting the chloride with terephthaloyl chloride to form N,N'-di-p-n-butoxyphenacylterephthalimide, and (5) reacting the imide with phosphoryl chloride to form the final compound.

The preparation of 1,4-bis(5-p-n-butoxyphenyloxazol-2-yl)-benzene and its intermediates is disclosed as follows. The starting material in the preparation is p-n-butoxyacetophenone.

To a stirred solution of p-n-butoxyacetophenone (23.0 g) in ethyl ether (200 ml), bromine was added. First, 0.6 ml of bromine was added and the solution was stirred until the bromine color vanished. Then another 1.0 ml was added and the solution was again stirred until the bromine color disappeared. Finally, 5.0 ml of bromine was added over a period of 5 minutes followed by 10 minutes of stirring. The pale yellow solution obtained at the end of the bromine additions was washed twice with water, dried overnight with sodium sulfate and evaporated to a colorless, mobile gum. A nuclear magnetic resonance spectrum was obtained and indicated 85% conversion to p-n-butoxyphenacyl bromide.

All of the p-n-butoxyphenacyl bromide was dissolved in chloroform (60 ml) and hexamethylene tetramine (14.0 g) in chloroform (15 ml) was added. The mixture immediately warmed but, after 3 hours, deposited only a few milligrams of material. A precipitate was produced by dropping the solution slowly into a large excess (600 ml) of rapidly stirred ether. The thus produced precipitate was filtered and washed with water. Analysis of the precipitate showed that it was a quaternary salt of p-n-butoxyphenacyl bromide and hexamethylene tetramine. Calculated for C.sub.18 H.sub.27 N.sub.4 0.sub.2 Br: C 52.6; H 6.57; N 13.64 and Br 19.43%. Found: C 52.89, 52.66; H 6.77, 6.85; N 13.52, 13.54 and Br 19.67, 19.38%. The quaternary salt melted at from 127.degree. to 128.degree.C. The nuclear magnetic resonance spectrum in deuterochloroform on a Varian XL-100-15 spectrometer showed triplets at .delta. values 1.00 and 3.98 (--CH.sub.2 CH.sub.3 and OCH.sub.2 CH.sub.2 --) along with a broad absorption 1.1 to 2.1 (aliphatic --CH.sub.2 -- chain), a singlet at 5.50 (--COCH.sub.2 --N+) and an aromatic A.sub.2 B.sub.2 spectrum at 6.82, 6.92, 8.00 and 8.09. The hexamethylene tetramine signal was split into a singlet at 5.99, 6 protons [-N (CH.sub.2).sub.3 .tbd.] and an AB quartet centered at 4.70, 6 protons [.tbd.N.sub.3 (CH.sub.2).sub.3 ] with a coupling constant of 14 cycles between the axial and equatorial protons. A yield of 40.5 g (near quantitative) of the salt was obtained. It could be used directly in the next stage of the preparation or could be crystallized from a large volume of acetone.

The hexamethylene tetramine quaternary salt of p-n-butoxyphenacyl bromide (40.0 g) was stirred vigorously in ethanol (320 ml) and concentrated hydrochloric acid (40 ml) was added. The reaction mixture was allowed to stand overnight and deposited a large quantity of solid. More ethanol (250 ml) was added. After 60 more hours the reaction mixture was warmed gently and filtered. The precipitate was washed with 50 ml of warm ethanol. p-n-Butoxyphenacylammonium chloride (20.1 g -- 85% yield) was precipitated as a white powder by slowly dropping the alcohol solution into 3.0 l of dry ether. The precipitate was filtered and dried. The nuclear magnetic resonance spectrum in deuterium oxide at 60.degree.C on a Varian A-60 spectrometer showed triplets centered at 1.10 and 4.05 (--CH.sub.2 CH.sub.3 and --O CH.sub.2 CH.sub.2 --), an aromatic A.sub.2 B.sub.2 system at 6.80, 6.95, 7.75 and 7.90, a singlet at 4.68 (--CO CH.sub.2 N--) and a broad absorption around 1.70 (aliphatic --CH.sub.2 -- chain). Integrated intensities were in accord with the structure of p-n-butoxyphenacylammonium chloride. p-n-Butoxyphenacylammonium chloride (20.0 g) and terephthaloyl chloride (8.0 g) were refluxed in dry pyridine (150 ml) in the absense of moisture for one hour. The mixture was then cooled and poured, with stirring, into water (500 ml) and the solid was filtered, washed with water, dried and recrystallized from 500 ml of pyridine. A white crystalline solid (7.7 g -- 35% yield) was obtained. The solid, upon analysis, proved to be N,N'-di-p-n-butoxyphenacylterephthalimide. Calculated for for C.sub.32 H.sub.36 N.sub.2 O.sub.6 : C 70.6; H 6.62; N 5.14%. Found: C 70.66, 70.41; H 6.68, 6.56; N 5.20, 5.14%. The nuclear magnetic resonance spectrum (A-60) in deuterodimethyl sulfoxide at 105.degree.C clearly showed triplets centered at 0.87 and 3.94 (CH.sub.3 CH.sub.2 and --O CH.sub.2 CH.sub.2 --), a singlet at 4.55 (--COCH.sub.2 NH--), an A.sub.2 B.sub.2 aromatic quartet at 6.72, 6.86, 7.63 and 7.78 (terminal aromatic protons) and aromatic singlet at 7.69 (central aromatic ring).

N,N'-di-p-n-butoxyphenacylterephthalimide (6.0 g) in phosphoryl chloride (280 ml) was refluxed overnight. Unreacted phosphoryl chloride was evaporated under reduced pressure. Yellow crystals (4.6 g -- 82% yield) of 1,4-bis(5-p-n-butoxyphenyloxazol-2-yl)-benzene were obtained from 1.6 l of glacial acetic acid. Calculated for C.sub.32 H.sub.32 N.sub.2 O.sub.4 : C 75.4; H 6.28; N 5.50. Found: C 75.21, 75.17; H 6.44, 6.37; N 5.24, 5.29. The melting point was 217.degree.-217.5.degree.C. Saturated solutions of 1,4-bis(5-p-n-butoxyphenyloxazol-2-yl)-benzene in dimethyl sulfoxide, dioxane and 2-methoxyethanol were prepared and pumped by means of a nitrogen laser. The dye lased in the blue to blue-green regions.