BuI]. Mater. Sei., Vol. 21, No. 2, April t998, pp. 121-126. Indian Academy of Sciences. Growth of anthraquinone crystals by gel aided solution technique and their characterization K RAJENDRA BABU, M DEEPA, C M K NAIR* and V K VAIDYAN* Department o~" Physics, University of Kerala, Kaziuvattom, Thiruvananthapuram 695 581, India ;Department of Physics, M.G. College, Thiruvan~thapurarn 695 004, It~dia MS rexcelved 9 September 1997; revised 28 November I997 Abstract. Anthraquinone, an oxidation product of anthracene, has been gro~na by gel aided solution technique employing sodium metasilicate. Needle shaped crystals were oblained in 0,5% (w/v) solution of anthraquinone for pH 5-S, The grown crystals were characterized by optical microscopy~ SEM, IR~ UV and XRD. Keywords. Gel; solutiort; antlu:aquinone; crystal growth; oxidation; photoreaetton. 1. Introduction acetone ratios (2 : 1, 3 : 1, 4 : I). The mixture was allowed to set. The mixtures with higher pH (>6.5) were set Derivatives of anthrace~e are convertible to other com- within 48 h, wlxereas those with lower pH (5) took nearly pounds by direct oxidation. Anthraquinone comes under one week. Over the set gels, 0.5% (w/v) solutiot~ of this class of conkoounds. Considerable work has been anthracene in acetone was it~corporated as top solution. reported on the synthesis of anthraquinoue by catalylic The samples were kept open to diffuse sunlight, Few oxidation of anthraquinone (Ivan and William 1949; samples were kept in a dark room. Owens I958; Noboru et al 1969; Cn-ozev et al 1976; Chung 1978; l)as and Nikhilendti 1982; Malik and 3. Results and discussion Dohnal 1990; Pielichiouski et al 1992). The mesopositions in anthracene acquire the numbers 9 and '10. respectively. It was observed that the level of top soltltion decreased The successful outcome of the reaction is due to the stightly during the first, week due to slow ewtporation special reactivity of the me~opositions and the greater and diffusion into the gel. Tiny transparent crystals were stability of anthraquinone. The double bonds in the observed floating on the surface of the top solution. central ring are rendered inert by incorporation of oxygen Within two weeks, yellow needles were found growing in the terminal benzene rings (Louis and Mary 1960). from the tiny transparent crystals. Formation of yellow Anthraquinone exhibits optical and photosemiconducting needles of anthraquinone is found to depend on several properties in addition to third harmonic generatiQn (Yao factors. An important parameter which determined the 1962; Grozev et al 1976; Mizogucb.i and Venishi 1991). yield of anthraquinone was the concentration of anthra- Anthraquinone crystallizes in the monoclinic sysEem cene solution kept over the gel. Higher concentration with space group P21/a (a=1.581, b=0.3942 and (3 %) of anthracene solution produces a large number of c =0.7865 am) with two molecules per unit cell. Here, anthracene crystals on the gel surface and tiny needles we report the growth of anthraquinone observed during of anthraquinone were formed after a long period (-two the growth of anthracene by the gel aided solution months). A better yield of anthraquinone resulted in a technique (Rajendra Babu et al t998). The grown crystals solution of concentration 0.5% '(w/v) within two weeks. are characterized by optical microscopy, SEM, IR, IYV A typical sample of gel, adjusted for pH 5, over which and XRD. a few yellow needles of anthraquinone were formed is shown in figure IA. In this case, tiny crysLals formed 2. Experimental on the stlrface of the top solution moved down to gel surface and yellow needles ef anthraquinone were ~own The chemicals used in this study were of BDH/AR from them. In certain other gel samples when the illu- grade. Sodium metasilicate of gel density 1.05 gemS; mination was high, large number of yellow needles were was prepared, treated with glacial acetic acid in the pH obtained. range 5-7-5 and mixed with acetone for different gel Organic crystals can be grown from a wid.e variety of solvents, but since these solvents are non-aqueous, *.Author for correspondence pH cannot be used as crystallization vm-iable (Margaret 121 t22 K Rajendra Babu e~ at ) Figure I. (~k) Needles of an'ihraqui~onc seen growing in the supern~tant so]ution kept over th~ gel, (B) a needle of anthraqulnone grown from a clnster of mlthracene crystals, (C) micrograph of needles obta.ined under crossed nico] prism, (D) a single c~,stai o~',ja'nthraquinone photogr~phed in straight extinction position with nicol in 45 ~ (1i;) micragraph showing the. growth of a largc number of yellow rleeAles of anthraqulnone in accton~--water solution of amhmcene and (F) SEM photograph of a nee.die of anthtaquinone. .,,,,, Growth qf anthraquinone crystals 123 et a[ 1986). However, in the present study, crystals were By the irradiation of anthracene in acetone, anthraquinone formed only in the top soIution of particular pH (~ 6), is obtained as a final product as represented by the irrespective of the gel pH. Hence, pH of top solution folIowing conversion (figure 3). and in turn pH of the gel should have some effect on investigation on the solvent (acetone) incorporated over the nucleation cff anthraquinone. Crystals of anthnNuinone ~lle gel in this experiment revealed that there was a were found to grow in atl pH values tried (5, 5.5, 6, gradual increase in the density, surface tension arid 6.5, 7 and 7.5). But, better yield was obtained in 5-6 conductance of the solvent. Hence, it can be presumed range. Most f:wourable pH was 5-5 in which yellow that such changes might have modified the anthracene needles were found to grow into the gel medium in solution favourably for being converEed into anthra- addition to that in the top solution. The rate of growth qui none by photoreaction. Density measurement of solvent of these needles were studied. A uniform increase in and solution (table t) showed that the supernatant solution the growth rate of needles into the gel medium was of mathracene undergoes a change similar to the behaviour observed up to six days. After one week, the crystals of acetone-water mixture. Thus the supernatant solution attained maximum size, with a lower growth rate. This might have been tuned for the growth of yellow needles. was followed by dissolution of crystals and the size of The differences in growth of anthraquinone in pure gel crystals fluctuates as shown in figure 2. and acetone mixed gel is also noted. When the solution The samples kept in darkness did not yield yellow was kept over pure gel, the changes in supernatant crystals of anthraquinone, but only platy crystaIs of solution was fast m~d resu]ted in the nucleation and anthracene. This confirms that the yellow needles of growth of large number of anthracene crystals. Solution anthraquinone were produced by the photoreaction over the acetone-mixed gel was found to undergo a slow of mathracene as reported earlier ('Corey and Taylor 1964-). change in parameters and few anthracene crystals were 1 1.2 / E 1.0 E / ,=,4 0.8 / 0.6 0.4'0:/ / J I i I I I i I L i i t i 0 40 120 200 280 350 440 520 Time (hours) Figm'e 2. Growth klaedcs of an[hraquinone crystal. ~ ----~[~ "% 02hu C3L) Anthracene Anthraceneperoxide Anthra quinone Figure 3. Photoreaction of anthracene. I24 K Rqje,~dra Babu et ol formed. Within this time the solution is tuned for easy Table 2. IR spectral data ot" anthraquinone. photoreaction and growth of anthraquinone. In order to have better understanding of the role played Yellow acedlcs Yellow needles by water-acetone system, water was mixed with acetone grown Jn acetone grown in acetone~. sofutlon kept river water mixture by in different proportions. This mixture was used to prepare the acetone mixed solution growth anthracene solution so as to grow crystals by slow gel (am-t) (cm% Assign mcnts evaporatlor~ without the aid of gel. A notable observation was that yellow needles of aathraquinm}e were lbrmed in acetone-water system only if a seed was added, Good 937 935 (-2]-[ Oltt OI" piano 8 [0 810 bending yield (figure 1E) was obtained when the mixture con- taining 5-30% of water was kept in an illuminated room. 62l Skeletal detbrm The crystals were sepm'ated, washed, dried and charac- 694 690 Ring breathing terized with X-ray powder diffraction, IR, UV-visibte I 170 1160 CH in plarie bm~ding spectroscopy, optical and scanning electron microscopy. ] 284 1280 1304 1330 Ring stretching 1332 1470 Table 1. Density of soivent/so[ution at 3we. 1473 1560 1522 1620 Density 1(~35 S oJven t/so lu t~on (gcm -3) 1591 1580 Aromatic vibrations Pure acetone 0.753 of qulnones Acetone kept over the gel !br one week 0.895 1653 1678. C=O stretch ur Saturated solution o[" anthracene in acetone f).764 1676 quinones Top ,solution in which anthraqtlinone is tBrmcd 0-847 100 (a] 95 90 85~ 80 '75 70 g 4,--' 100 {b) t E 95 ,E-- j,-.. 90 85 - 80,- 70[ 1 [ ~ __ i 4000 3200 24 00 1600 800 Wavenumber {crn 1 ) Figr,re 4. inJ'rwed spectrum ot-" anthraquJnone needles grown (a) in acetone sotLmon incorpomtezl over acetone mixed gel and (b) in acetone-water solution. Growth of anthraquinone crystal,r 125 4, Characterization none nucleated from anthracene crystal substrate. Hollow cavity of the anthraquinone is also seen in the ct3'stal. 4.[ Optical at~d scanni~tg electron microscopy Figure 1C gives the micrograph of certain needles of Optical micrographs c~t" the single crysta[s of anthraquinone anthraquinot~e obtained under crossed nicol position.