TITRATIONS IN NON-AQUEOUS SOLVENTS

WATER, as SOLVENT WATER, as SOLVENT ADVANTAGES: ☻ cheap, clean (can easily be purified) ☻ high relative permittivity (ε): good solvent DISADVANTAGES:  °C temperature range  apolar substances can not be disolved  K w = 10 −14, therefore K d ≤ 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):H 2 SO 4, CH 3 COOH, HCOOH, acetoneproton donor AMPHOTERIC (amphiprotic):H 2 O, alcohols, acetonitrile BASIC (protophyl):pyridine, liq. NH 3, amins, dioxaneproton acceptor APROTIC:liquid SO 2 INERT:CCl 4, CHCl 3, benzene, carbohydrates

REACTIONS in NON-AQUEOUS SOLUTIONS AUTOPROTOLYSIS EQUILIBRIA determines the ionic product : 2 H 2 O  H 3 O + + OH − 10 − ☻ neutralization (protolytic solvents)≈ 90 % ☻ complex formation, precipitation, redox≈ 10 % solventKpH scaleneutr. point 2 CH 3 COOH  CH 3 COH CH 3 COO − 10 − ,5 2 NH 3  NH NH 2 − 10 − C 2 H 5 OH  C 2 H 5 OH C 2 H 5 O − 10 − ,5 − pH scale depends on the value of K HL = [H 2 L + ][L − ] NEUTRALIZATION ANALYSIS in NON-AQUEOUS SOLVENTS

REACTIONS in NON-AQUEOUS MEDIUM E.g. HClO 4 + pyridine (Py) in glacial acetic acid acid:HClO 4 +CH 3 COOH  ClO 4 − +CH 3 COOH 2 + K = [CH 3 COOH 2 + ][CH 3 COO − ] = 10 −13 base:Py +CH 3 COOH  PyH + +CH 3 COO − ClO 4 − + CH 3 COOH 2 + PyH + + CH 3 COO −  PyH +  ClO 4 − + 2 CH 3 COOH 2 CH 3 COOH − Brönsted equation can be used − reactions take place through reaction of acids or bases with the solvents

ADVANTAGES of USING NON-AQUEOUS SOLVENTS ☻ 1 More than 3 acids/bases can be measured in mixture due to the wider pH range ☻ 1. More than 3 acids/bases can be measured in mixture due to the wider pH range compared to water E.g. methyl-ethyl-ketonewater pH range pH range 5 comp. measurablemax. 3 acids (3 x ΔpH(4) = 12) HClO 4 - HCl - Salicylic acid - Acetic acid - Phenol (can titrated with TBAH (C 4 H 9 ) 4 N + OH − )

☻ 2. Differentiation - levelling effect (K d ~ 10 −12 can be measured) a)Differentiation effect: in water: HClO 4 ≈ HCl ≈ HNO 3 in CH 3 COOH: HClO 4 > HCl > HNO 3 in HF:medium > weak > base acid Conclusions: Strong acids (in water) can separetely be measuredin acidic solvents Strong bases - ″ - in basic solvents in water: HCl > CH 3 COOH > benzoic acid b)Levelling effect: in pyridine: HCl ≈ CH 3 COOH ≈ benzoic acid EXPLANATION by the protonaffinity ADVANTAGES of USING NON-AQUEOUS SOLVENTS Conclusions: Weak acids (in water) can be measured in basic solvents Weak bases - ″ - in acidic 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 ADVANTAGES of USING NON-AQUEOUS SOLVENTS  expensive  volatile  toxic  removal of water is necessary, can take water (humidity) from the air DISADVANTAGES of USING NON-AQUEOUS SOLVENTS

−HClO 4 in glacial acetic acid − HClO 4 in glacial acetic acid − HCl in propylene-glycol /chloroform mixture STANDARD SOLUTIONS ACIDIC : BASIC : −TBAH (C 4 H 9 ) 4 N + OH − )in pyridine − TBAH (C 4 H 9 ) 4 N + OH − ) in pyridine − KOH in ethanol application: - weak bases: K b : 10 −7 − 10 −12 e.g. aromatic amines, amides, alcaloides, etc. 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.) application: - weak acids: K a : 10 −7 − 10 −12 e.g. carboxylic acids, phenols, enols etc. e.g. carboxylic acids, phenols, enols etc. - high-molecular-weight organic acids, that have limited solubility in water limited solubility in water

END POINT DETECTION CHEMICAL:(INDICATORS) −crystal violet (in glacial acetic acid) − crystal violet (in glacial acetic acid) INSTRUMENTAL: −potentiomety : glass electrode in glacial acetic acid − potentiomety : glass electrode in glacial acetic acid − conductometry −phtaleins (phenolphtalein) (e.g. in pyridine) − phtaleins (phenolphtalein) (e.g. in pyridine) −azo compounds (methyl red) (e.g. in alcohol) − azo compounds (methyl red) (e.g. in alcohol) R +  C-R  R ibolya R + R-H 2+  C-R + H + C - R  R R ibolya zöldeskék R + R-H 2+ R-H 3+  C-R + H + C - R+ H + C-R  R RR-H violet green yellow