TITRATIONS IN NON-AQUEOUS SOLVENTS
WATER, as SOLVENT
ADVANTAGES:
DISADVANTAGES:
☻ cheap, clean (can easily be purified)
☻ high relative permittivity (ε): good solvent
 0 - 100 °C temperature range
 apolar substances can not be disolved
 Kw = 10−14, therefore Kd ≤ 10−7 unmeasurable
WATER actively participates in all type of reactions:
- acid and base: acid-base reactions take place through connection
to water first (amphoteric)
- complex formation: cations: aqua complex
anions : H-bond
- precipitation: dissolves precipitate of ionic lattice (high hydration energy)
- oxidant and reductant; range of redox potential:
0 −1,23 V theoretical
-0.8 − 2,1 V practical
CLASSIFICATION of SOLVENTS
ACIDIC (protogene):
H2SO4, CH3COOH, HCOOH, acetone
proton donor
BASIC (protophyl):
pyridine, liq. NH3, amins, dioxane
proton acceptor
AMPHOTERIC (amphiprotic): H2O, alcohols, acetonitrile
APROTIC:
liquid SO2
INERT:
CCl4, CHCl3, benzene, carbohydrates
REACTIONS in NON-AQUEOUS SOLUTIONS
☻
☻
neutralization (protolytic solvents)
≈ 90 %
complex formation, precipitation, redox
≈ 10 %
NEUTRALIZATION ANALYSIS in NON-AQUEOUS
SOLVENTS
− pH scale depends on the value of KHL = [H2L+][L−]
AUTOPROTOLYSIS EQUILIBRIA determines the ionic product :
solvent
2
2
2
2
H2O  H3O+ + OH−
CH3COOH  CH3COH2+ + CH3COO−
NH3  NH4+ + NH2−
C2H5OH  C2H5OH2+ + C2H5O−
K
10−14
10−13
10−32
10−19
pH scale
neutr. point
0 - 14
7
0 - 13
0 - 32
0 - 19
6,5
16
9,5
REACTIONS in NON-AQUEOUS MEDIUM
− Brönsted equation can be used
− reactions take place through reaction of acids or bases with the solvents
E.g. HClO4 + pyridine (Py) in glacial acetic acid
acid:
K = [CH3COOH2+][CH3COO−] = 10−13
HClO4 + CH3COOH  ClO4− + CH3COOH2+
base: Py
+ CH3COOH  PyH+ + CH3COO−
ClO4− + CH3COOH2+
PyH+ + CH3COO−
2 CH3COOH
 PyH+ClO4− + 2 CH3COOH
ADVANTAGES of USING NON-AQUEOUS SOLVENTS
☻ 1. More than 3 acids/bases can be measured in mixture due to the wider pH range
compared to water
E.g.methyl-ethyl-ketone
water
0 - 25.7 pH range
0 - 14 pH range
5 comp. measurable
max. 3 acids (3 x ΔpH(4) = 12)
HClO4 - HCl - Salicylic acid - Acetic acid - Phenol
(can titrated with TBAH (C4H9)4N+OH−)
ADVANTAGES of USING NON-AQUEOUS SOLVENTS
☻ 2. Differentiation - levelling effect (Kd ~ 10−12 can be measured)
a)
Differentiation effect:
in water:
HClO4
≈ HCl
> HCl
≈ HNO3
in CH3COOH:
HClO4
> HNO3
in HF:
medium > weak > base
acid
b)
Conclusions:
Strong acids (in water) can separetely be measured in acidic solvents
Strong bases
- ″ in basic solvents
Levelling effect:
in water:
HCl
> CH3COOH
> benzoic acid
in pyridine:
HCl
≈ CH3COOH
≈ benzoic acid
Conclusions:
Weak acids (in water) can be measured in basic solvents
Weak bases
- ″in acidic solvents
EXPLANATION by the protonaffinity
ADVANTAGES of USING NON-AQUEOUS SOLVENTS
☻ 3. Determination of organic acids and bases which have a limited solubility in water.
☻ 4. Application of new reagents and indicators is possible due to
DISADVANTAGES of USING NON-AQUEOUS SOLVENTS

expensive

volatile
 toxic
 removal of water is necessary, can take water (humidity) from the air
STANDARD SOLUTIONS
ACIDIC :
− HClO4 in glacial acetic acid
− HCl in propylene-glycol /chloroform mixture
application: - weak bases: Kb : 10−7 − 10−12
e.g. aromatic amines, amides, alcaloides, etc.
- high-molecular-weight organic bases, that have
limited solubility in water
E.g. Determination of „Lidocain” (Lidocainum Ph.Hg. VII.)
CH3
C2H5
NH
CO
CH2
N
C2H5
CH3
BASIC :
− TBAH (C4H9)4N+OH−) in pyridine
− KOH in ethanol
application: - weak acids: Ka : 10−7 − 10−12
e.g. carboxylic acids, phenols, enols etc.
- high-molecular-weight organic acids, that have
limited solubility in water
END POINT DETECTION
− phtaleins (phenolphtalein) (e.g. in pyridine)
CHEMICAL:
(INDICATORS) − azo compounds (methyl red) (e.g. in alcohol)
− crystal violet (in glacial acetic acid)
R ++

C-R

R
ibolya
violet
+ H+
R-H 2+

C-R
+ H+

R
zöldeskék
green
INSTRUMENTAL:− potentiomety : glass electrode in glacial acetic acid
− conductometry
R-H 3+

C-R

R-H
yellow