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Meeting 8 (Condensed Key)
1. a. The 2,6-dimethylnitrobenzene is the oxidizing reagent and stannous chloride is used as the reducing reagent in the reaction. The nitrogen atom in the nitro group is reduced from its (+3) oxidation state to (-3) oxidation state, which requires six electrons per nitro group. Thus, three equivalents of SnCl2 (stannous chloride) are required per nitro group because each tin(II) is oxidized to tin(IV) in the reaction, which is a two electron step .
RNO2 + 3 SnCl2 + 7 HCl -----> RNH3+Cl- + 3 SnCl4 + 2 H2O (R=2,6-(CH3)2C6H3)
b. Concentrated hydrochloric acid is the main source of protons for the reaction above. In addition, stannous chloride dissolves better in conc. hydrochloric acid than in water.
c. The reaction of the xylidinium salt with potassium hydroxide releases the free amine (2,6-dimethylaniline=2,6-Xylidine) in an acid-base reaction.
R-NH3+ + OH- -----> RNH2 + H2O
The desired pH-value is pH>10 to ensure that the ammonium salt is completely deprotonated.
d. The product is a base (primary amine), which would absorb much stronger on acidic drying agents like anhydrous sodium sulfate or anhydrous magnesium sulfate. Potassium carbonate is used as drying agent because the compound displays a lower affinity towards a basic drying agent.
e. A vacuum adapter is required to provide a pressure exchange during the distillation. It is placed between the water-jacketed condenser and the receiving flask.
2. a. The procedure in the reader asks to use 1.1 equivalents of the acyl chloride. The given amount of 2,6-dimethylaniline is equal to 8.93 mmol (=(1.10 mL*0.9842 g/mL)/(121.18 g/mol). Thus, 9.83 mmol of the acetyl chloride should be used, which is equal to 0.78 mL (=(9.83 mmol*112.94 g/mol)/1.42 g/mL).
b. Acyl chlorides are very reactive and among other compounds also react with water (i.e., moisture) to form the corresponding carboxylic acid.
ClCH2COCl + H2O ---- > ClCH2COOH + HCl
c. Glacial acetic acid is used as solvent because it does not introduce water into the system. In addition, the unreacted ammonium salt is soluble in glacial acetic acid.
d. The signal at δ=7.9 ppm is due to the amide proton, which is significantly shifted because of the electronegativity of the nitrogen atom, which also bears a partial positive charge due to the amide resonance.
e. The signal due to the amide proton shifts to δ=9.3 ppm in DMSO-d6 due to the strong hydrogen bond of the amide proton with the oxygen atom of the DMSO.