Synthesis of An Inorganic Experiment Christopher Tillman and Gary L. wood' Valdosta State University, Valdosta, GA 31698 Michael Hampton University of Central Florida, Orlando, FL 32816
The synthesis of main group ring systems is an important part of any inorganic laboratory course. The prime example of such a compound is cyclotriphosphaz(V)ene ([Cl3P=NI3). While the preparation of this compound is straightforward, the characterization of the product by NMR requires a n instrument capable of observing 31P NMR. Here, we describe a related system, cyclodiphosphaz(V)ane ([C13P-N(R)I2),whose synthesis is summarized by eq 1.The product is characterized by 'H NMR and demonstrates heteronuclear coupling ( 1 ) .
cous membrane irritants (2). All these materials should be handled in a fume hood. Results and Discussion An example of the 'H NMR recorded in deuterobenzene on a 200 MHz instmment is shown in the figure and the NMR data are summarized in the table. The spectrum reveals three different proton environments that can be related to the primary (-CH3), secondary (-CH2-) and tertiary (-CH-) carbon groups. The spectrum i s a good example of heteronuclear coupling because the hydrogens attached to the secondary carbon (CH9-, " , show roto on-uhosnhorus counline (3JHp= 30 H;) and proton-proton coupling (3Jm= 8 Hz) resulting i n a doublet of tripHCI (') lets. All other proton environments show only proton-proton coupling. While t h i s spectrum was obtained on a 200 MHz instrument, acceptable spectra can be ohtained using a 60 MHz continuous wave instrument. This experiment provides the student the opportunity to synthesize a n inorganic rin compound under anhydrous conditions and assign both Jm and 3 J ~ coupling p in the 'H NMR spectrum. The procedure can be run with a "nitrogen blanket" in place of the calcium chloride drying tube. The substitution of other primary amines also is possible but care should be taken to avoid amines with branches a t the carbon alpha to the nitrogen (such as isopropyl amine)
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Experiment This experiment should be performed in a fume hood. A 250-mL, three-necked, round-bottomed flask is fitted with a reflux condenser to which a CaC12 drying tube is attached, a pressure equalized addition funnel, and a ground glass stopper. Into this flask is placed 10.41 g of phosphorus pentachloride (PC15), 100 mL of carbon tetrachloride and a stirring bar. Asolution of isobutylamine (3.65 g i n 50 mL of carbon tetrachloride) is placed in the addition funnel. The amine solution is added dropwise to the C C l f l C l ~ mixture with stirring, a t room temperature, over a period of 15 min resulting in the formation of a cloudy solution. The solution i s then warmed to 70 "C and allowed to stir for 12 to 24 h. During this time a large amount of HCl is evolved and the solution clears. At the end of this time, the heat is removed and the solution is allowed to cool to room temperature. The solvent i s then removed by vacuum evaporation or rotary evaporator. The resulting solid is recrystallized from a minimum volume of cold (0 "C) carbon tetrachloride. Typical yield is 30% (theoretical yield is 50% based on phosphorus pentachloride). The isolated product is a clear, crystalline solid that i s slightly moisture sensitive and fumes on contact with moist air. The melting range for the product is 104-107 "C in a sealed capillary tube. The product is soluble is benzene, toluene, and chloroform.
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NMR Data Summary
Species -CHZCH(CH3)z -CHzCH(CH3)z -CHzCH(CH3)2
Chemical Shin (ppm) Coupling (Hz) 'JHP = 30 (triplet) 3.3 3~~~ = 8.0 (doublet) 2.5 3~~~ = 8.0 (multiplet) 1.0 3~~~ = 8.0 (doublet)
Caution: Carbon tetrachloride (CC14)is a suspected human carcinogen. Phosphorus pentachlaride (PCIS)and isobutyl are severe eye, skin, and muamine ((CH3)2CHCH2-NH2) 'Author to whom correspondence should be addressed.
200MHz 'H NMR of [CI~-PN(CHZ)CH(CH~)Z]~ Volume 72 Number 6 June 1995
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because these will result in the formation of a monophosphaz(V)ene.
CHE-8068881 t h a t made possible the purchase of the Varian Gemini 200 MHz NMR spectrometer for the Universitv of Central Florida.
Acknowledgment The work at
Literature Cited
State University was supported by Research grant C-2696' The authors also wish to acknowledge National Science Foundation grant
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Journal of Chemical Education
1. Allcock. H. R.Phosphorus-Nitrog~n Compounds;Academic Press: New York, 1972. 2. Sax.NI17lng:Lewis.RichardJ.HozardourChemicoisDeakRejpmnce:VanNostrand ~einhold:~ e ~wo r k 1987. ,
