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stating from Moo3powder, which is cheaper than the eonventional (NH4)6M07024. 4H20. using the common 24% (13 M) instead of 15% (8 M)NH1solution. adding the reagents kquentially by weighing, which facilitates the work up. ending the washings with diethyl ether so that drying the prcduct is more rapid. i
A Typical Run In a 5-mL conical vial (on an electronic balance) is placed 0.25 g (1.7 mmole) of Moo3 powder, 0.40 g H20 and 0.40 g (5.5 mmole) 24% NHs (Pasteur pipet). The mixture is stirred with a glass rod for about one min to obtain a clear colorless solution (exothermic reaction). Then, 0.75 g (7.5 mmole) of 2,4-pentanedione is added. and the mixture is stirred; however, two phases remain: Finally, 1 g (10 mmole) of 63% HN03 is added dropwise (exothermic reaction). The mixture is cooled to mom temperature while stirring and the solid formed is ground until a yellow powder results. (Powdering the initially lumpy precipitate improves the purity of the product and requires less than 5 min.) The product is filtered through a Hirsch funnel, washed consecutivelvwith distilled water (4 x 2 mL). ethanol ( 2 x 2 mL)and peroxide-free diethyl ether (2 x 2 mL), and dried in air. Washings also may be done by decanting. The powder settles sufficiently in less than 1 min so that more than 75% of the liquid can be removed. Using a Pasteur pipet is advisable in this case to reduce product losses c aforms c ) ~ a supernatant skin every time because M ~ O ~ ( a . water is added. The entire process requires about 30 min. About 0.19 g of a light yellow finely powdered product melting at 179 f 1 "C (the reported value) is obtained. The IR spectrum of the compound shows two strong bands at 900 and 930 cm-I corresponding to the stretching vibrations characteristic of the cis-~00'arran~ement. &nglets a t 2.12 and 2.14 6 (CD2C12, room temperature), assignable to the two sets of inequivalent methyl groups (see drawing), are observable in the 'H NMR spectrum.
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Microscale Preparation of AICI) Francisco J. Arndlz Laboratorio de Quirnica lnorgtmica Universidad de Burgos 09001 Burgos (Spain) Aluminum chloride is a very common chemical that may be prepared by several procedures ( I ) , including that recently reported for the synthesis of a number of anhydrous halides (2).AlC13is rarely prepared to be used as starting material for other experiments because it is available at low cost. However, it is very moisture sensitive, and special care is required in handling pure samples. Purification prior to use (usually by sublimation) is frequent. When a small amount of anhydrous MC13 is needed for microscale synthesis (or as a catalyst for reactions that might be aborted with deactivated MCls), the method described here represents a convenient alternative to others. It is based on the reaction of aluminum iodide, prepared in situ, with alkylchlorides (31, as represented in simplified form (CH& is formed and the excess Al is reacted) in the equation below. Al + 3/2 I,
+ 3 CH2CI2-t AlC1, + 3 CH,ICI
Anhydrous CHzClz is the solvent of choice by availability and low cost, but especially because the reaction proceeds smoothly. The reaction can be conducted conveniently with inexpensive materials. A typical run is described. A 5-mL ampoule is charged consecutively with 50 mg (1.85 mmol) of pure aluminum foil cut in fine strips (10-15 pieces), 2 mL of CH2C12,and 650 mg (2.56 mmol) of dry Iz. The ampoule (A) is connected to a T tubing (T) that is further assembled (the figure, part a) to the gas line (or to an inflated balloon) and to a 50-cm long bent tubing (kc.)as an air condenser and connected to a bubbler (B). The system is flushed with 1-2 L of an inert gas (argon, nitrogen, or dry air), the clamp (C) is closed, the reactant
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Acknowledgement I am grateful to the editor for helpful comments. Llteratum Cited 1. See, e. g.: (a1 Srivastava,A.; Ma.Y.; Panhayatselvan,R.; D i n e , W.;Nicholss, K M. J C k m . Soe.,C k m . Commun. lssP,853.~bIB~to~,C.;Mmzur,C.;CerriUo,n.; Robert, F:Oaueerh, P.I n o n Chem. 1984.33, 1421. ~ ~ ~ dn. ~ ~synth.~
2. chakrsvorti, M. c.; l s s ~29,129. , A8
Journal of Chemical Education
b)
I~ d h ~ ~ ~ , Schematicdiagramsfor (a)the preparation and (b) washing of AiCI, under an inert atrnospheri
mixture is refluxed until all iodine is consumed (15-30 min, visual color loss) and then for an additional 30 min to insure that the aluminum excess is dissolved. During this process a significant amount of CHzClzmay be lost (the air condenser is not very effective with this volatile solvent);if so, a new portion of solvent should be added (e.g., by injection through a rubber connection) to restore the original volume. The white powdered microcrystalline product (AICIJ is washed with CH2Clz(three 2-mL portions) and dried in vacuo. The washing may be achieved conveniently in a dry atmosphere once the giass tubing is disconnected bv removing the solvent with a Pasteur pipet. The pipet should havea glass wool plug, as shown in the figure part b. Paper or cotton plugs are unadvisable because AlC13reacts with, and strongly adheres to, these materials. 180 mg of pure AlC13 were obtained. Anal. Calcd for AlC13: Al, 20.23; Cl, 79.77. Found: Al, 20.1; CI, 79.5. Iodine test (Hz02 on the solid) negative.
In ring substitution of aromatic amines, the amino group acts as a powerful activator and an ortho-/para- director. However, in the strongly acidic nitration media, the amine is converted into anilinium ion; substitution is thus controlled not by the -NH2 but by the -NH3+ group which, because of its positive charge, is a strong ring deactivator and directs of the substitution to the meta- oosition (4. ~ ~ - - much . . 5).I t is possible, however, to direct the nitration reaction to the ortho- position by first protecting the amino group in the acetanilido form (i.e., acylation),carrying out the nitration reaction. then de~rotectingthe amino group by hydrolysis (see reaction). ~
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Literature Cited
Microscale Electrophilic Aromatic Substitution of pToluidine lsmail 0. Kady East Tennessee State University Johnson City, TN 37614
Although many organic chemistry experiments deal with electrophilic aromatic substitution, few illustrate the principles of group protection, substituents' effect on reactivity, and reaction orientation ( 1 3 ) .In this paper we present microscale experiments that allow first-year organic chemistry students to apply group protection and study the effect of ring substistuents on the reaction orientation in the nitration of disubstituted aromatic amines. These experiments incorporate common synthetic organic transformations and techniques which involve: (a) nitration of unprotected p-toluidine, (b) protection of amino group, (c) nitration of protected p-toluidine, and (dl deprotection of amino group. Most of the reactions involved are relatively fast and are complete in 30 min. In each experiment, it is possible for the student to determine the extent of the reactions by comparing the physical and spectral properties of reactants and products. Although the methods and techniques presented are adapted from basic organic chemistry laboratory texts such as those of Marmor ( I ) and Brewster (21, these experiments use simple glassware, common chemicals, and standard microscale procedures. All reactions give good yields of products to allow recrystallization and proton NMR analysis. Comparison of physical and spectral properties of the products enable the student to demonstrate the relationship between ring activation and reaction orientation in electrophilicaromatic substitution. Procedures for the microscale reactions and purification of products are described below. Therefore, these experiments can be incorporated easily into a first-year microscale organic laboratory cumculum. This paper was presented in part at the 13th Biennial Conference on Chemical Education, Lewisburg, PA, 1994.
CH3
6
Experimental Nitration of p-Toluidine
Dissolve 107 mg (1.0 mmole) of p-toluidine in 0.2 mL of concentrated HzS04 in a dry micro test tube. Shake the tube until all the solid dissolves; then cool in ice. Carefully and dropwise add 0.4 mL of a solution consisting of concentrated HN03 (0.3 mL) and concentrated HzS04 (0.1 mL), while keeping the temperature of the reaction mixture below 5 "C. After the addition is complete, allow the reaction Volume 72 Number 1 January 1995
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