1. Baker reagent grade N,N-dimethylformamide was used without purification.

2. The submitters employed, without purification, 98% ethylenediamine obtained from Mallinckrodt Chemical Works; the checkers employed material from Eastman Organic Chemicals, which was redistilled (b.p. 117–118°) before use. The amount of ethylenediamine employed is sufficient to provide three equivalents of diamine for each mole of chromium(II) and to neutralize any acid remaining in the chromium(II) perchlorate solution.

3. The submitters employed a 1.64 M solution of chromium(II) perchlorate, prepared by stirring a mixture of 5.7 g. of pure chromium metal pellets (United Mineral and Chemical Corporation, 129 Hudson St., New York, 10013) with 60 ml. of 20% perchloric acid under a nitrogen atmosphere at 30° for 12 hours.^2,3 The rate of dissolution of the chromium metal is increased if the metal is washed successively with concentrated hydrochloric acid and water just before it is added to the perchloric acid. The checkers employed a 0.519 M solution of chromium(II) perchlorate, prepared in a comparable manner with chromium metal obtained from the Mining and Metals Division, Union Carbide Corporation. The deep-blue solution of chromium(II) perchlorate is transferred to a storage vessel with a siphon or a hypodermic syringe, and the solution is stored under a nitrogen atmosphere in a vessel fitted with a rubber septum. Provided this solution is protected from oxygen, it is stable for long periods of time; aliquots for standardization or reaction are conveniently removed with a hypodermic syringe. The solution is standardized by adding 5.00-ml. aliquots to excess 1 M iron(III) chloride followed by titration of the iron(II) ion produced with standard cerium(IV) sulfate solution, using phenanthroline as an indicator. [Org. Synth., Coll. Vol. 5, 993 (1973)]. The submitters had recommended use of only slightly more [2.3 moles of chromium(II) complex per mole of halide] than the stoichiometric amount of chromium(II) complex in this reduction. However, because these concentrations of reagents lead to a very slow reaction rate in the last 5–10% of the reduction (Note 6), the checkers found it more convenient to employ excess reducing agent [3.8 moles of chromium(II) complex per mole of halide].

4. 1-Bromonaphthalene, m.p. 2–4°, obtained either from the Aldrich Chemical Company, Inc., or from Matheson, Coleman and Bell was used without further purification.

5. A slow stream of nitrogen was passed through the N,N-dimethylformamide for 30 minutes to remove any dissolved oxygen.

6. The progress of this reaction may be followed by quenching aliquots of the reaction solution in acidic aqueous ammonium sulfate followed by extraction with ether and analysis of the ethereal extract by GC. With a 1.2-m. GC column packed with silicone fluid, No. 710, on Chromosorb P and heated to 215°, the retention times of naphthalene and 1-bromonaphthalene were 1.9 minutes and 6.7 minutes, respectively. The submitters employed a 30-cm. GC column packed with Porpak P for this analysis. Since the presence of even 5–10% of unchanged 1-bromonaphthalene makes purification of the naphthalene difficult, it is important that the reduction be complete before the product is isolated. With reaction conditions described in this preparation [0.100 mole of ethylenediamine, 0.0080 mole of 1-bromonaphthalene, 60 ml. (0.031 mole) of 0.519 M chromium(II) perchlorate, and 80 ml. of N,N-dimethylformamide], the checkers found that reduction was usually complete in less than 15 minutes. Under the conditions [0.032 mole of ethylenediamine, 0.0040 mole of 1-bromonaphthalene, 5.5 ml. (0.0090 mole) of 1.64 M chromium(II) perchlorate, and 40 ml. of N,N-dimethylformamide] originally suggested by the submitters, a reduction time of approximately 3 hours was required for complete reduction.