Inorganic Liquid Ammonia Essay

Submitted By Andre-Rebelo
Words: 1433
Pages: 6

To: Professor
From: Andre Rebelo

Drew University
Department of Chemistry
Chem 342L­ Advanced Inorganic Chemistry Date: March 2015 CC:

Experiment 4: Synthesis of P h2CH 2CH 2Ph2 in Liquid Ammonia and H and P NMR and Melting Point

In this experiment, the preparation of a solution containing solvated electrons is achieved by dissolving sodium metal (2.3g, 0.1 mol) in liquid ammonia. This sodium­ammonia solution was used to induce the reductive cleavage of a phenyl group from triphenylphosphine to form sodium diphenylphosphide, which under our reaction conditions will precipitate from the solution as a yellow solid. Further additions of 1,2­dichloroethane produces
1,2­bis(diphenylphosphino)­ethane. The synthesized compound can act as a chelating bidentate ligand and be used in organometallic chemistry to stabilize low­valent transition­metal centres.
The verification of formation was conducted by taking a melting point and NMR ( H ). The literature value states1,2­bis(diphenylphosphino)ethane melts at 137­142 C. The synthesized product (shiney white crystal solid) had a melting point range of 139­142 C strongly indicating the formation of dppe. Roughly, 0.169 g of 1,2­bis(diphenylphosphino)ethane was formed correlating to a percent yield of 0.4 %. Of course, additional data was need and thus, the NMR taken present show peaks at 1.3 ppm, 2.3 ppm and 7.1­8.0 ppm, which is the necessary evidence to prove the formation of 1,2­bis(diphenylphosphino)ethane. Introduction: In chemical laboratories, liquid ammonia can extensively be utilized as a non­aqueous solvent, as a medium for reductions. Since, liquid ammonia contains hydrogen bonding interactions it will have unusual properties that allow it to dissolve compounds not readily soluble in water. Anhydrous liquid ammonia, for example has the chemical properties to dissolve certain high reducing metals including alkali, alkaline and lanthanide metals. The addition of electropositive metals to liquid NH3 creates a deep blue color characteristic of solvated electrons. It is important to mention at high concentration of electropositive metals such as sodium a color change can occur from deep blue to a bronze brought out by the solvent electrons. In a reaction with sodium metal any indication of transformation of reagents is apparent when the intense blue color disappears. In our experiment, sodium metal is used along with liquid ammonia to create a sodium­ammonia solution to acts as a strong reducing agent to add two electrons to triphenylphosphine. In that process of moving electrons a cleavage occurs between a C − P bond in triphenylphosphine producing sodium diphenylphosphide by which a reaction with 1,2­dichloroethane synthesizes 1,2­Bis(diphenylphosphino)ethane. The reaction sequence can be seen below in figure one.

Figure 1: Reaction Scheme: 1­ Formation of Sodium­Ammonia Solution: Na(s) + NH3(L) → N aNH2 + H2 ­Used as a reducing agent to add two electrons to triphenylphosphine. Intense deep blue solution. 2. Cleavage of Carbon­ Phosphorus Bond: P (C6H5)3 + 2Na → NaP(C6H5)2 + NaC6H5
N aC6H5 ­ conjuga te base of benzene­ quickly deprotonates ammonia to N aNH2 must be neutralized. ­ via N H4Br forming a sodium salt and additional liquid ammonia ­ color change occurs: Deep blue to an intense red­orange.
­ Color fluctuates to a bronze­red orange­ orange
­ Product One
N aP(C6H5)2 ­ Product Two
­ Yellow carney salt
­Soluble in polar solvents. (dichloromethane) 3. Addition of 1,2­Dichloroethane 2NaP(C6H5)2 + C2H2Cl2 → (C6H5)2PCH2CH2P(C6H5)2

In conducting the experiment, we hope to gain familiarity with the non­aqueous solvents and bidentate ligands. In addition, familiarity in laboratory techniques