solution is concentrated to about 50 mL. In order to avoid an excess, which prevents the crystallization of the salt, a lack versus the stoiehiometric amount of benzyltrimethyl ammonium hydroxide (35 g of a commercial 40 wt % solution in methanol) is added to the henzodithioie acid solution. The mixture is evaporated to dryness under vacuum. The deep purple or violet crystals of benzodithioic ammonium salt are washed with cold hexane and dried at room temperature (yield 70-80%). Characteristics:mp = 87 'C; 'H NMR (6, CDsOD, TMS): 3.05 (s, 9H N(CH&); 4.50 (8, 2H, CH2); 7.30 and 8.20 (m, 5H phenyl ring); 7.55 (s, 5H, henzyl ring). UV-visible (THF) A,, = 516 nm (log c = 2.12); 368 nm (log c = 3.83).
ume is adjusted at 100 mL with the solvent mixture. Methanol facilitates the dissolutionof the salt 1 and prevents the precipitation of the quaternary ammonium chloride during the reaction, which disturbs the measurements. The kinetics is monitored at 516 nm (cell 1cm, ref. THF); theabsorbance (At)ofthe solution ismeasured ever" 5 min for an hour. Absorbance for t = 0 (An)and fort = ( A J can be determined graphically by extrapolstion can the curve A, = f(1,. According tu theslope of the curve
Nucleophilic Substitution of Halogenated Compounds with 1 Salt 1 (3.03 g, 10 mmol) in THF (30 mL) is stirred with the stoiehiometric amount of halogenated compound at room temperature for 2 h. It does not matter if some crystals remain undissolved, since dissolution will occur during the reaction. The color of the solution changes from deep purple to bright red (discolorationwith epichlorohydrin) as the henzyltrimethylammonium halide precipitates. After filtration and evaporation of the solvent, the reaction mixture is diluted with several milliliters of hexane and cbromatographed on Si01(-15 g in a 0.5-in.-diameter column), using hexane or hexsneTHF according to the solubility of the product. Red products are collected and are recrystallized from methylene chlaride and hexane, with yields around 75%. Physical ondlHNMR characteristics ( 8 , CDCb, TMS) of benzodithioates: 3-Chlorupropylbenrudithioatr (3). Eluant: hexane; redoil bp = 104 'C tdec) 2.10(m, 2H,(.Hz,; 3.50 and :I60 (dl, 4H, CH-CI, nnd C H.A I..: 7.GOand 8.10 lm. ohenvl . . 5H. .. . erounr .. Ethylene his(benzodithioate) (4). Eluant: hexsneTHF 80-20, mp = 105 'C; 3.70 (s, 4H, CH2); 7.50 and 8.10 (m, 5H, phenyl rind. ~ e t h ~ l ehis(benzodithioate) ne (5). Eluant hexane-THF 80-20, mp = 124 O C ; 5.40 (a, 2H, CH2),7.50 and 8.10 (m, 5H, phenyl
a second-order rate constant is easilv found (first order toward each reactant). Found: k = 3 . i 0 - ~mollmin a t 25 O C ; ordinate for origin: 0.96; (correlation coefficient 0.993).
.
-----,.
2-Butenyl benzodithioate (6). Eluant: hexane; red oil hp (0.1 mm) 130-132 ' C ; 1.70 (d, 3H, J = 6 Hz); 3.90 (d, 2H, J = 7.5 Hz); 5.40 and 6.10 (m, 2H, alefinic H); 7.20 and 8.10 (m, 5H, phenyl ring). l-Phenyl-7-oxa-2,6-dithiahicyelo[2.2.l]hept(7). Eluant: hexane:. mn: . 82-83 "C. The ABX svstem exhibits a null eoupling constant between two protons making a 909 dihedral angle (JAX= 0)according tothe Karplusrule (10).Thisis easily shown witha Dreiding model; 3.30 (d,2H, JAB = 9 HZ);3.70 (dd, 2H, JAB = 9 HZ,JBX = 5.5 HZ);5.80 (t, lH, JBX = 5.5 Hz); 7.50 and 7.70 (m, 5H, phenyl ring). Kinetic Study with ~ ~ i c h l o r o h ~ d r ~ i n In a 100-mL volumetric flask, 1 0 mmol (0.303 g) of salt 1 is dissolved in 80 mL of THF-methanol (80-20). The stoichiometric amount of epichlorohydrin (0.096 g) is added quickly and the vol-
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Quaternary ammonium benzodithioates provide a variety of possibilities for student experiments. T h e time required for each experiment is convenient for laboratory session, and collecting the results obtained by students working on homologous benzodithioates or with different reagents affords the possibility of obtaining a broader view of the multiple facets of the nucleo~hilicsubstitution. Different hrominated compounds ran be used for the synthesis of the salt (bromochlorot~enzene,bromoanisole, bromntoluene,etr.) in order tosrudy further the influenceof the suhstituent on the reactivity of the salt (1.2). Starting materials are inexpcnsiw, commerrially availat~lecom~~ounds.'l'hey are used without further purification. Synthesized productsaresafe: somedithiocarboxylates have been patented for skin protection from IJV radiation (11). In 1985. the averaee cost for the svnthesis of a benzodithioate salt and its reaction with a halogenated compound is estimated t o FF. 60.00 (-US58). t h a t is. FF. 30.00 (US54) for one student per session. Literature Clted I. Bonnsns-Plaiaance, C.; Gr-ier, J. C.: Leuesque, G.:Mshjoub, A. Bull. Soc. Chim. Fmnce 198L5.891. 2. ~onnsna-Plai&n&& Iavesque, G. Makromol. Chsm., 1986,187,2841. 3. Bonnsns-Plai-ce. C.; Gressier, J. C.; Levesque. G. Mokromol. Chem. Rapid Corn. mun. 1983.4.337.Gr-ier.J.C. J.MoeromoleeulorSri.Chem. 1986.A23(11),1263. 4. Roth, J.P.; Rempp,P.:Psrrod,J. J.Polym.Sci. 1984,Cd.1347. 5. Schoufs, M.; Meijer, J.;Verrneer, P.: Brandsma,L.Synthesis 1978,439. 6. Beiner, J. M.: Thui1licr.A. C. R. Acod. Sei. Pork 1912,274,642 and references cited. 7. 86hrne. H.;Sall, K.Bsr. 1948,81,123. 8. Cohen,T.;Ruffnor.N. J.:SchuU,D.M.:Fogd.E.R.:Falek. J.R.Orp.Synlh.1979.59, 202.
9. Leon, N. H.: Asquith, R. S. Tefrnhadran 1970,26,1719. 10. Bovey, F. A. Nuclear Magnetic Resonome Spectroaeopy;Autdemie: New York, 1969: P 135. 11. Reneh Patent
2396545, 1977: Mullcr.
D.; Leveaque,
0. Cham. Abatr. 1919, 90,
P127404v.
A "Tea Bag" Drying Technique Drying organic liquids implies in most cases a tedious filtration step in order to remove the drying agent. We have simplified this procedure by placing the drying agent in a "tea hag" made with filter paper and tied with a suitable fiber such as nylon, polypropylene,or cotton. The organic liquid is introduced into a flask along with the "tea bag", whose string is caught by a stopper or a septum. Once the liquid is dry, the drying agent is simply pulled out. Nicholas M. lrvlng CINDEV
Apartado 282-C, Zona 15 Guatemala. Guatemala
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J. rnal of Chemical Education
