Question

Give the reaction of the following the liquid NH3 as solvents protolysis of amino acids​

Answer 1

Answer:

Despite low boiling point (-33.4oC), easy to handle.

Solubilities, relatively high dielectric constant (ammonia, eo= 26.7 @ -60oC;

water, eo = 82 @ 18 deg.C).

=> ionic compounds can be soluble but the lower eo compared to water means that salt with highly charged,

non-polarisable anions such as carbonates, sulphates, and phosphates are insoluble.

NH3 is more polarisable than H2O,

so salts with more polarisable anions are more soluble,

hence the solubility trends.

F- < Cl- < Br- < I-

PO43- < SO42- < OAc- < NO3

specific solvation: NH3 is a better a-donor than H2O and ammine complexes are formed,

especially with the later transition (Ni2+, Cu2+) and B metals (Ag+, Zn2+).

Hence higher solubilities for compounds of these metals than those of the A-metals.

Self-ionization of ammonia is much "weaker" than water.

2NH3 NH4+ + NH2- k @ 223K ca. 10-30

Liquid ammonia will therefore tolerate very strong bases such as

C5H5- which would otherwise be hydrolysed in water.

Ammonia is kinetically stabilized to reduction (but easily oxidized)

by many reagents, e.g., the reaction;

Na + NH3 NaNH2 + H2(g)

is very favourable but slow in the absence of a catalyst such as Fe3+.

Reactions and applications

Solvolysis: synthesis of amides

OPCl3 + 6NH3 OP(NH2)3 + 3NH4Cl

SiCl4 + 8NH3 Si(NH2)4 + 4NH4Cl

Metatheses reactions: solubility reversals

In water,

RCl + AgNO3 AgCl(ppt) + RNO3

In ammonia

AgCl + KNO3 RCl(ppt) + AgNO3

Ba(NO3)2 + 2AgCl BaCl2(ppt) + 2AgNO3

Alkali metals in liquid ammonia

Sodamide as a base

Na + NH3 NaNH2 + H2(g)

NaNH2 + C5H6 NaC5H5 + NH3

NaCp (useful reagent)

Solvated electron as a reducing agent (Birch reduction),

many examples of compounds in very unusual low oxidation states.

[Ni(CN)4]2- + Na/liq-NH3 [Ni(CN)4]4-

Fe(CO)5 + Na/liq-NH3 [Fe(CO)4]2-

Mo(CO)6 + Na/liq-NH3 [Mo(CO)4]4-

[Pt(NH3)4]2+ + Na/liq-NH3 [Pt(NH3)4]

Reduction of salts of Group IV and V elements give polyhedral anions, many examples.

Ge94-, Sn52-, Sn93-, Pb52-, Bi42-, P72- As64-