In the Laboratory
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A Practical Procedure for the Solid-Phase Synthesis of Azo Compounds in the Undergraduate Organic Laboratory Cailan Wang,*† Xiaoxia Wang, Yulu Wang, Xiaoyang Wang, and Hong Wang Department of Chemistry, Henan Normal University, Xinxiang 453002, P.R.C.
We present an opportunity for undergraduate students to carry out a solid-phase reaction to prepare a new type of azo compound. The reaction can be achieved at a rapid rate with a simple workup. By doing this experiment, undergraduate students can learn new concepts such as the new synthesis method, the preparation of a new type of azo compound, and the practice of the uses of the products. Organic solid-state reactivity is a fascinating subject. Its methodology has many advantages, such as high efficiency and selectivity, easy separation and purification, mild reaction conditions, and environmental acceptability (1, 2). The method is widely used in a variety of organic syntheses involving substitution (3), condensation (4), oxidation–reduction (5, 6 ), rearrangement (7), and elimination (8). However, its use in the synthesis of azo compounds has not been reported. We have found that a new type of azo compound can be easily synthesized under solid-state conditions. Here we report this convenient and rapid solid-phase method using ferric nitrate to oxidize N-(4′-ethoxyphenyl)-2-phenyl hydrazinecarboxamide (1a) for the synthesis of N-(4′ethoxyphenyl)-2-phenyl diazenecarboxamide (1b), and to oxidize 2,2′-diphenyl-carbonic dihydrazide (2a) for the synthesis of phenyl-2-phenylhydrazide diazenecarboxylic acid (2b). This reaction is very rapid, and the end point can be easily judged by the color change of the reactant mixture. Compound 1b can be used as dye, and compound 2b is a widely used reagent in analytical chemistry (9, 10). The experiments are designed to demonstrate the uses of these azo compounds. The entire experiment can be completed within a three-hour period. The synthetic route is shown in the following scheme: Fe(NO3)3•9H2O
EtO
NHCONHNH
Solid phase
1a
EtO
NHCON
N
1b
• C AUTION: The mixture should be ground as fully as possible. Hydrochloric acid (1:1) should be kept nearby in case of a spill or skin contact. Azo compounds should be kept away from the skin and clothing.
Synthesis of the Azo Compounds A mixture of compound 1a (0.271 g) and Fe(NO3)3⭈9H2O (0.808 g) was ground in a mortar. Within 2–3 minutes, the color of the mixture changed from white to light brown. The reaction mixture was extracted with acetone (10 mL) and a few drops of hydrochloric acid (1:1) were added to the acetone solution until the solution color changed from brown to red. Cold water (15 mL) was added and an orange-red flocculent product was precipitated. The product was isolated by filtration, washed three times with 15-mL portions of water, and dried under vacuum to give 0.256 g of N-(4′-ethoxyphenyl)-2phenyl diazenecarboxamide (1b): yield 95%, mp 128–129 °C (lit. 127–129 °C ). Its structure was characterized by elemental analysis and by IR and 1H NMR spectroscopy. Phenyl-2-phenylhydrazide diazenecarboxylic acid (2b) is synthesized in a manner similar to that described above: yield 91%, mp 154–156 °C (lit. 155-156 °C ). Its IR and 1H NMR spectra are available to confirm the structure. Demonstration of the Uses of the Azo Compounds A piece of white cloth is soaked for 2 min in a solution of 0.1 g of compound 1b dissolved in 5 mL of acetone. After the acetone is evaporated, the color of cloth does not fade when the cloth is washed in water. Compound 2b (0.2 g) is dissolved in 100 mL of ethanol and an orange-red solution is obtained. A drop of this solution is added to four test tubes, each of which contains 1 mL of a 10-µg/mL solution of either ZnCl2, CuCl2, AgNO3, or NiCl2. The color changes from orange-red to violet-red with Zn2+, and to violet with Cu2+ or Ni2+; there is no change with Ag+. Acknowledgment
Fe(NO3)3•9H2O
NHNHCONHNH
Experimental Procedure
We are grateful for the financial support from the Natural Science Foundation of the PRC and Henan Province.
Solid phase
2a
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NHNHCON
N
2b
Supplemental Material
Supplemental material for this article is available in this issue of JCE Online. Literature Cited
†
Current address: Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716.
1. Organic Solid State Chemistry; Desiraju, G. R., Ed.; Elsevier: Amsterdam, 1987; p 179. 2. Rasmussen, M. O.; Axelsson, O.; Tanner, D. Synth. Commun.
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