Analytical applications of thiosemicarbazones and semicarbazones: A review

ANALYTICAL APPLICATIONS OF THrOSEMICARBAZONES AND S~MICARBAZON~S: A REVIEW R. B. SINGH, B. S.GARG and R. P. SINCH Department of Chemistry, University of Delhi, Delhi-l 10007. India (Receiaed 18 May 1977. Reoised 20 Jarzuury 1978. Accepted 21 March 1978) Summary-The

analytical applications of thiosemicar~~zon~s and semicarbazdnes are reviewed.

Thiosemicarbazones (TSC) and semicarbazones (SC) are a class of compounds obtained by condensing thiosemicarbazide or semicarbazide with suitable aldehydes or ketones. The active grouping for chelation is shown below in structure (r):

‘C=N*-NH-C-N’ R’4

;li;

\

‘R

2

\MJ (1) when

X = 0, semicarbazone X = S, thiosemicarbazone

Thiosemicarbazones and semicarbazones act as chelating agents for metal ions by bonding through the sulphur or oxygen atom and the hydrazino nitrogen atom marked with an asterisk in (I). In a few cases they behave as unidentate ligands by bonding only through the sulphur or oxygen atom. Domagk et nf.’ reported for the first time the anti-tu~rcular activities of metal thiosemicarbazones and semicarbazones. Since then a number of papers have appeared on the pharmacology of these compounds. The metal-TSC complexes were found to be active against influenza,’ protozoa,3 smallpox4 and certain kinds of turnours’ and to be very good pesticide8 and fungicides.’ The activity of TSC is thought to be due to their power of chelation with traces of metal ions present in biological systems. The anti-tubercular activity of p-acetamidobenzaldehyde thiosemicarbazone is found to be enhanced by the presence of small amounts of copper ions.* Depending upon the type of aldehyde or ketone used for condensation, TSC and SC can act as unidentate, bidentate or multidentate chelating agents for metal ions, producing highly coloured complexes. These coloured complexes are then used in selective and sensitive determination of metal ions. The aim of this review is to summarize these analytical applications.

Preparation

qf the reagents

Semicarbazones are obtained by condensing semicarbazide hydrochloride with suitable aldehydes or ketones in presence of sodium acetate. Sometimes hydrochloric acid must be present in the preparation of semicarbazones.9 Thiosemicarbazones are prepared by condensing thiosemicarbazide with an aldehyde or ketone in the presence of a few drops of glacial acetic acid. Preparation of the mono-derivatives is simple but the di-derivatives are a little difficult and require treatment. Dipyridylglyoxal dithiosemispecial carbazone” was prepared by cyclizing the monoderivative with 6M hydrochloric acid, for example.

Chemical properties Just as hydrazones are weaker bases than hydrazines, semicarbazones and thiosemicarbazones are weaker bases than semicarbazides and thiosemicarbazides respectively. Hydrolysis of these compounds yields first the hydrazones, hence these compounds resemble hydrazones in many of their reactions. Mild reductions of semicarbazones and thiosemicarbazones yield l-substituted semicarbazide and thiosemicarbazide, respectively. Catalytic reduction of these compounds yields hydrazides are further hydrolysed to hydrazines. Reaction with alkoxides such as sodium ethoxide converts semicarbazones into hydrazones, and with a strong base, hydrocarbons are obtained. This reaction may be applied for replacement of the carbonyl group by a CH,-group. The reagents can be readily hydrolysed to give the original carbonyl compound and hence are often useful for identification and isolation of carbonyl compounds. A method of obtaining the equivalent weight of the parent carbonyl compound is to hydrolyse the semicarbazone with aqueous hydrochloric acid and titrate with standard iodate solution.’ ’ 619

R. B. SINGH, B. S. GARG and R. P. SINGH

620 ANALYTICAL

APPLICATIONS

The various thiosemicarbazones carbazones which have been used reagents are summarized in Table 1. Applications

determine Mo(VI) in presence of iron in highly acidic medium.52 Extraction of the complexes not only increases the sensitivity but is also helpful in simultaneous determination of metal ions. Dipyridylglyoxal dithiosemicarbazone” reacts with Ni(I1) and Co(H) at pH 5.2, but only the Ni(I1) complex is extractable into chloroform, and hence allows the determination of both metals when present together. Biacetyl monoxime thiosemicarbazone has been used to determine Bi(II1) in presence of Cu(II), by extraction of the complex into isobutyl methyl ketone.38 Presence of EDTA’ 5,18,28 is sometimes necessary for completion. Cyclohexane-1,2-dione dithiosemicarbazone has been used to determine Cu(I1) in alkaline medium, alkaline tartrate medium and

semiand as analytical

in spectrophototnetry

Semicarbazones and thiosemicarbazones form coloured metal complexes in conditions ranging from moderately acidic to moderately alkaline. Only a few are used to determine metal ions in highly acidic medium. 3-Hydroxypicolinaldehyde thiosemicarbazone is used to determine Co(H) in highly acidic medium.” Similarly glyoxal dithiosemicarbazone reacts with Ag(1) and Hg(l1) at pH 1.1.28 Salicylaldehyde

thiosemicarbazone

has

been

used to

Table Abbreviation PAT PAS DPGT DPKT MPKT PAPT APPT MPAT HPAT GDT APT HMAPS HMAPT DAPT BAMOS BAMOT BAMOPT BAMT DBAS DBAT NBAT AMBAT DABAT ESBAT SAS SAT HNAT TAS TAT PADT PIDT FAT NFAS PTFA NQT-4S NQS-4S PQMT SAPT I .2 CDDT I.3 CDDT FACT TBPK IT BTDD LS FPDT

Structure II II III IV V VI

VII VIII IX X XI XII XII XIII XIV XIV xv XVI XVII XVII XVIII XVIII XVIII XVIII XIX XIX xx XXI XXII XXIII XXIV xxv XXVI

XXVII XXVIII XXVIII XXIX xxx xxx1 xxx11 xxx111 XXXIV xxxv XXXVI XXXVII XXXVIII

1.

Systematic

name

Picolinaldehyde thiosemicarbazone Picolinaldehyde semicarbazone Dipyridyl glyoxal dithiosemicarbazone Di-2-pyridyl ketone thiosemicarbazone Methyl-2-pyridyl ketone thiosemicarbazone Picolinaldehyde-4-phenyl-3-thiosemicarbazone 2-Acetylpyridine-4-phenyl-3-thiosemicarbazone 6-Methylpicolinaldehyde thiosemicarbazone 3-Hydroxypicolinaldehyde thiosemicarbazone Glyoxal dithiosemicarbazone Acetophenone thiosemicarbazone 2-Hydroxy-5-methylacetophenone semicarbazone 2-Hydroxy-5-methylacetophenone thiosemicarbazom 2,4-Dihydroxyacetophenone thiosemicarbazone Biacetyl monoxime semicarbazone Biacetyl monoxime thiosemicarbazone Biacetyl monoxime 4-phenyl-3-thiosemicarbazone Biacetyl monothiosemicarbazone 2,4-Dihydroxybenzaldehyde semicarbazone 2,4_Dihydroxybenzaldehyde thiosemicarbazone 4-Nitrobenzaldehyde thiosemicarbazone 4-Acetamidobenzaldehyde thiosemicarbazone 4-Dimethylaminobenzaldehyde thiosemicarbazone p-Ethylsulphonylbenzaldehyde thiosemicarbazone Salicylaldehyde semicarbazone Salicylaldehyde thiosemicarbazone 2-Hydroxy-1-naphthaldehyde thiosemicarbazone o-Thymolaldosemicarbazone Thiophene-2-aldehyde thiosemicarbazone o-Phthalaldehyde dithiosemicarbazone Phthalimide dithiosemicarbazone 2-Furaldehyde thiosemicarbazone 5-Nitro-2-furaldehyde semicarbazone 4-Phenyl-3-thiosemicarbazone of 2-furaldehyde 1,2-Naphthoquinone-2-thiosemicarbazone-4-sulphonic acid 1,2-Naphthoquinone-2-semicarbazone-4-sulphonic acid Phenanthrequinone monothiosemicarbazone Salicylaldehyde-4-phenyl-3-thiosemicarbazone 1,2-Cyclohexanedione dithiosemicarbazone 1,3-Cyclohexanedione dithiosemicarbazone Furylacrolein thiosemicarbazone when R = 2-fury1 and R’ = H, R = Ph, 2-furyl, 5-methyl-2-fury], 5-nitro-2-fury1 and R’ = H, Et 2-Benzothiazolylphenyl ketone thiosemicarbazone /$Ionone thiosemicarbazone Bisthiosemicarbazone of diethyl-3,4-dioxadioate Lawsone semicarbazone Furylpentadienal thiosemicarbazone

References 12-16 17 10, 18, 19 20 21 22,23 24 25,26 27 28 29 30,31 30,32, 33 34 17 35-39 40 41 42 43-45 46 46 47 48-50 51 52254 55, 56 57 58 59 60-62 63 64,65 66 9,67-70 67, 68, 69, 71 72 73 74,15 76 77, 78 79 80 81 82 83

Thiosemicarbazones Structures

621

and semicarbazones in Table 1

X

II H=N-NH-C-NH,

II

when

X = S, PAT X = 0, PAS

when

X = 0, HMAPS X = S. HMAPT

III

N-NH-C-NH,

IV

V -CH, S II N-NH-C-NH, S

VI

II

CH=N-NH-C-NHC,H,

VII S N-NH-&-NH&H, S

VIII

II

CH=N-NH-C-NH,

IX

OH CH=N-NH-I-NH

X

2

N-NH-C-NH,

S

II

II

N-NH-C-NH, CH, XI

C \ N-NH-C-NH, d

XII

CH,

N-NH-C-NH,

II

X

R. B. SINGH, B. S. GARG and R. P. SINGH

622

Structures

CH,-C--C-CH3 II II NOH N-NH-C-NH, II X

xv

in Table 1 (cm&.)

when

X = 0, BAMOS X = S, BAMOT

when

X = 0, DBAS X = S, DBAT

when

Y Y Y Y

when

X = 0, SAS X = S, SAT

CH,-C--C-CH, II 11 NOH N-NH-C-NH&H, II S CH3-C-C-CH,

XVI

II

0

II

N-NH-C-NH,

II

S XVII

CH=N-NH-C-NH, !

HO -8:

OH

XVIII

CH=N-NH-C-NH, b Y Jo

CH=N-NH-C-NH,

xx

OH

”

XXI

CH(CH,), XXII CH=N-NH-C-NH2

CH=N-NH-C-NH,

XXIII

0 a XXIV

d S CH=N-NH-k-NH, N-NH-C-NH,

xxv CH=N-NH-C-NH,

XXVI CH=N-NH-C-NH,

= = = =

NO,, NBAT -CH,CONH, AMBAT N(Me),, DABAT SO,Et, ESBAT

Thiosemicarbazones

Structures

and semicarbazones

623

in Table 1 (contd.)

XXVII

XXVIII when

SOsH XXIX

N-NH-C-NH,

xxx

CH=N-NH-C-NH-CsH, b OH

xxx1

N-NH-C-NH,

xxx11

N-NH-C-NH, II s S II N-NH-C-NH,

Q xxx111

R-CH=C-CH=N-NH-C-NH,

XXXIV @Z<&J

d

NH -j_N,‘N Z xxxv CH:CH-C-CH,

II

S

II

N-NH-C-NH,

XXXVI NH 2%HN-N

II C,H,O,C-CH,-C-C-CH,CO,C2Hs L-NH-C--NH

XXXVII

XXXVIII

N-NH-C-NH, II II

II s

2

X = S, NQT-4S X = 0, NQS4S

~--

MPAT

DPKT

DPGT

PAS

PAT

Compound

430

RhlIII)

OS(W) Pd(I1)

420 460 480 420

415 395

Co(B) CU~II)

OS(W)

620 39s

0.94 1.30

1.oO 1.13

I .96

0.93

0.7 1 0.66 1.17 0.91

0.56

350 350 345 400 550 590-610 630 410 410

I041.m01e~‘.cm-

1.40 0.74 1.90 0.58 1.40 2.20

nm

c,

~^__ 356 410 385 610 360 360 316

Fe(I1 j Ni(II)

Fe(H) Ni(I1) Co(H)

Ni(I1) Fe(H) Fe@) Cu(I1) AR(I) Ni,Cu, Fe, Co in mixtures Cu(II) Ni(I1) Co(H) Fe(III) Fe(H)

Co(H)

Ion

J-lnB1)

--

._

150-800 pg 50-500 pg

2.0

I:2 Heating is necessary

26

25 25 2s 26 1:2

1:2

20 20 I:2 111

20 20

19

1-S l-5

112

Simult. detn. of both Ni and Co by extn. of one complex at pH 5.2. Also used for anal. of mixt. of Co and Ni and industrial catalysts Ascorbic acid present 6.0-6.9 pH range is more sensitive

In presence of EDTA

I:2

C,H,.CH,OH

CHCI, CHCI,

I:2 1:l I:1 1:l 1:2

I:I

17 17 17 18 18 18 18 19

16

1-4 0.5-2.5

2-9 2- 7.5 2-8 l-5 l-7

0.3-1.5 O.2- 1.2 0.5-2.2

2.0

2.5-7.5 4.0-6.9 1.5-9.5 3.8-6.0 3.9-4.2 5.5-9.0 1.5 1.5

5.2 5.2

2.5 5 10.0 IO.0

10.0

10.0

9.5

In presence of EDTA Binary, ternary and quarternary mixtures analysed

13 14 14 13 15

Refs.

112 1:3 I :2 I:1 1:f

Remarks

7.2 10.7 9.4-12.3 3.9-7.9 8.9-10.7

M:L

12

Extraction 112

data

5.6-9.5

PH”

Limit of determination, pw*

Table 2. Spectrophotometric

390 400 335 335 650 610 395 418 490 590 390

Ni(I1)

325 356 335 410 345 335 545 345 375 350 360 550

Fe(II1)

Co(I1) Ni(I1) Fe(I1)

HMAPT

HMAPS

BAMOT

BAMOPT

600

Cu(I1) Fe(I1)

Cu(I1) Bi(II1) Mn(II1) Co(I1) Ni(I1) Fe(I1) Cu(I1) Mn(II1)

400 645

Cu(I) Co(H)

Ag(I) Hg(II) Fe(I1) Fe(H) Fe(II1) Cu(I1)

DAPT

APT

APPT

GDT

0.27 1.77 1.71 1.76 1.27 0.36

0.49 0.88 1.45 1.45 1.06

2.00

2.40 0.83 0.37 0.37 1.40

4.30 4.40 0.68

2.99

390

Co(H)

PAPT

0.46

430

Re(V)

MPKT

2.35 0.78

Co(H)

450

Ion

HPAT

Compound

~,*,, nm

5.0 9.5 5.3 5.3 8.559.5 2.5-3.5 9.2-10.3 3.888.0 5.2-10.0 4.0-9.3 8.5-9.7 10.0

3.6 2.2

7.9

2212

8-22

l-4.5 l-8.0

Amy1 ale.

IBMK

I:2 I:I

0.025-2.5 mg 0.558.0 ug

1:2 Variable 112 1:l 112

112 1:2 1:l 1:2

1:l

1:I 1:l

CH,Cl,

0.2-2 up to 5uM

0.02442.4 mg

C,H,

2-9

CHCI,

0.881.5 0.882.0

8-9 8-9 1.o-7.0 1.01-7.0 4.99 11 .o 5.6-9.8 5.0-6.0 Alk. med. Alk. med.

I:2 I:2 I :l I:1 1:2 I:2 112 I:2

I:2

CHCI,

0.222

1.0

1:I

36-38.8pM

2.4-6M

HCI

t:2 I:2

M:L

0.3-3.5 1.O-6.0

Extraction

7.0-9.0 1.op3.0

PH*

Limit of determination, ppm*

Table 2. (contd.)

medium

of EDTA of EDTA

were

Stability const. log/, = 4.0+ I In presence of NazEDTA (NH,),C,O, log/j = 5.3 10.1

PK,. pK2 and pK, 9.6, 11.2 and 12.4

Homogeneous

In presence In presence

pK,, pK,, pK, reported as 3.48, 6.76 and 10.75 respectively Redn. of Re(VI1) to Re(V) with SnCl, in 2.4-6M HCI Detn. of Ni and Co in mixture

Remarks

35 36 37 37 38 38 39 40 40 40 40 40

31

34 34 32

29

28 28 24 24 24 29

22 23

21

27

Refs

-.

SAS

SAT

1,3 CDDT

TAT 1,2, CDDT

FACT

6.3 6.3 6.3 6.3 6.3 6.3 cont. HCI 15

10.0 3-s

0.17

520

530 685

Fe(II1) Cu(II)

2.5-4.2 4.5-6,O

1”_28

0.74-6.0 l--l8

2.2--5.6 1.5-9.0 1.0-U

2.4-3.4

5.5

0.2-l .2 1.1-6.6 2.2-8.7

pg

l-5 OS- 2,s 1-S 35” 3.85 pg 1*2-~l4.7llg 0.s 8.6pg 0.6 12pg I-7.Opg 2-Y l-3.5 3.4-53 pg 6.2- 78ng

Limit of delerrnin~tl~~~l~ pp’n’

4.7

3 10 2.5-3.5

Acidic Acidic

io.0 11.4 8.6

PH*

2.32 2.80 1.42 1.32 1.92 2.27 Cl.40 0.48

0.47

3.90

3.95 6.25 0.41 0.57

z

3% 370 510 410 370 360

335 349 330 300 436 436 430 420 410 400 390 390 390 390 460 372 415 450 500 400 640 400 467

lo4 1.m& i_ cm -~.

t‘

Cu(I1) CofIf f Zn(iIl Ni(I1) Pd(I1) Pt(IVf Mn(I1) MO(W)

Ni(I1) Fe(H) Fe(II1) Cu(II)

Zn(I1) Co(II)

fU(lf)

OS OS Pd(i1) Cu(II) Ni(Il) I’d(H) Pt(II) Pd(II) I%(IY f

OS

Cu(I1) Ni(II) Co(H) Cu(II)

BAMOS

DBAT A MBAT NBAT DABAT ESBAT BAMT

Ion

Compound

&,X, lint

‘Table 2. (contrl.)

TBP

CHCI,

Extraction

1:2

I:1

I:1 1:2

1:l

M:L --______

1

MO and Fe can be detd. in presence of each other; alsoused in analysis of Ni-Cr and Mo-Fe alloys

alk. tart. or EDTA soln. pK,, 4.7; p#,, 10.05

Can be detd. in alk. med..

Water -DMF 9:

Slmultaneo~ls detn. is possible at two diiferent wavelengths pk’, = 10.6

30”,, ethanol

Remarks

52 51

76 76 76 16 16 76 53 52

84

75 75 75

7s 58 74 15

77 78

17 17 I7 43 46 46 41 48 41 41 77

Refs.

p

?J 7 ”

2..

I?;

6

x

f PJ

P m vl I

621

___

NNNPIN-

-mm

__

-----e-+--e

-“INC\(N-N

.,

.,

NQT-4S

NQS-4S

TAS

NFAS HMAPS HMAPT PQMT

Compound

Cu(I1) Zn(I1) Cd(I1) Hg(II) Ni(I1) Fe(I1) Fe(II1) Ni(I1) Cu(I1) Co(H) UWII) V(V) Pb(I1) Bi(II1) PO:MOO:wo:so:INi(I1) Cu(I1) Zn(I1) Cd(I1) In(II1) Pb(I1) Bi(II1) AI(II1)

Hg(II) Fe(II1)

IOll

1 ug-30 mg 65 ugg65 mg 20uggllOmg 40ugglOOmg 12 ugg60 mg

0.554.0 4.447.5 4.8-6.0 5.336.8 4.5-7.0 Addition of NaOH or HCI has no effect on complex 5.556.8 1.7-2.8 6.0-7.3 6.0-7.0 6.0&7.0 4.8-5.5 2.554.5 5.0-6.5 3.7.-6.8 5.5-6.8 5.5-6.8 4.0-6.0 5.556.8 1.772.8

0.1-207 mg O.lI20mg 0.5528.5 mg l-80 mg 12-50 mg 1.776.9 mg 0.6-4 mg 0.6-30 mg 0.6615.8 mg 0.6665 mg l-56mg 0.2-36 mg O.i-207mg 0.1~~105mg

up to 100mg

lmg

Limit of determination

2.0

PH

EDTA direct EDTA direct EDTA direct EDTA direct EDTA direct EDTA direct EDTA direct Hexamine/HNO, buffer, EDTA Dil. NHJHNO, buffer, EDTA Pyridine/HNO, or hexamine/HNO, Pyridine/HNO, or hexamine/HNO, Titration with Pb(NO,), Titration with Pb(NO,), in 305, methanol medium Titration with Hg(N03)2 in isopropyl ale. medium EDTA direct, non-reversible AcOH/HAc EDTA direct, non-reversible AcOH/HAc EDTA direct, non-reversible AcOH/HAc EDTA direct, non-reversible AcOH/HAc NaAC/HAC, EDTA direct Hexamine/HNO,, direct Hexamine/‘HNO,. direct Detd. by back-titration with Zn(I1 1

72 72 72 72 72 57 57 57 57 57 57 57 67 67 68 68 68 68 67 67 67 67 67 69 67 69 69

EDTA direct, also used for Cu in brass and gun metal and Ni in monel K and Brightway G

Red to colourless Red to colourless Red to colourless Red to colourless Red to colourless Deep red to colourless Deep violet to colourless Yellowish green to colourless Deep green to blue Yellow to colourless Blood red to light yellow Deep mustard to greenish yellow Purple to greenish yellow Purple to greenish yellow Greenish yellow to pink Greenish yellow to pink Greenish yellow to pink Greenish yellow to pink Purple to yellow Yellow to purple Yellow to purple Yellow to purple Yellow to purple Purple to yellow Purple to yellow Purple to yellow

Refs. 64 30

Remark EDTA direct EDTA direct

change

Orange to yellow Green to colourless

Colour

Table 3. Use as indicators

3.5 5.4 6.9 3.2 6.0

Ga Al Y Ga SC

HNAT DBAS

6.15-6.4

SC Zn

SAS

PH

Metal

I- 4 Fe(CN);-

PO:PG+fof.

Ga(III) Fe(II1) AI+Cu AI+Fe Al+Ga

IOll

Compound

Compound

412 360

370

Excitation max., nm

5.0-7.0 X0-6.0 6.0-7.0 2.5-4.0 0.3-2 ml of 0.2M hexamine 2-6ml of 0.2M hexamine

RH

472 425

455

Fhtorescence max., nm

2.5-65 ug 3.5-17ug 15-125 ug InM

0.002-0.02 ppm upto3ug

Range of determination

1:2 1:2 1:2 1:)

1:i 1:l

M:L

Remarks

NH,CI or (NH,)ZS04 necessary; titn. of std. Cd(I1) soln. with ferrocyanide

Detd. by back-titration with Zn(II) Detd. by back-titration with Zn(I1) AI-EDTA complex broken by NaF; and released EDTA titrated with Zn(I1). Also Al in bauxite AI-EDTA complex broken by NaF; and released EDTA titrated with Zn(I1). Also Al in bauxite Hexamine/HNO,, titn. with Pb(NO,), Hexamine/~NO~, titn. with PbfNO,), Hexamine/HNO~, titn. with Pb(NO,), Isopropyl ale, titn. of I- with Hg(II) (NH,),SO, or KC1 or K,SO, necessary, titn. of std. Zn(I1) soln. with ferrocyanide

Remark

O.m2-0.3% of SC detd. in allanite, mica, etc.

Also appl. to det. 0.002-0.004% of Zn(I1) in CdS04 and CdCI,, after sepn. of Zn(II) as thiocyanate into isoamyl ale.

Table 4. Fluorimetric applications

Purple to yellow

1.66159mg

12-50 mg 0.6-4 mg 2-42 mg

l-SOmg

Yellow to purple Yellow to purple Yellow to purple Yellow to purple Purple to yellow

Colour change

0.5-28.5 mg

Limit of determination

Table 3. (co&.)

51 51 51 56 31

51

Refs.

69 69 69 69 69 69 68 68 68 67 67

Refs.

el & g $. s: ;; A 8 2 B a. % B X;’

630

R. B. SINGH, B. S. GARG and R. P. SINGH

EDTA medium.84 It was generally observed that semicarbazones containing hydroxy groups ortho to the aldehyde group gave good colour reactions. Thiosemicarbazones are rather selective and sensitive for copper. Applications of these compounds for spectrophotometric investigations are summarized in Table 2. Applications

as visual indicators

The most common application is the direct titration of the metal against EDTA solution with thiosemicarbazones and semicarbazones as indicators. With o-thymolaldosemicarbazone,57 addition of acid or alkali has no effect on the complex formed. Phenanthraquinone monothiosemicarbazone” was used to determine Cu in brass and gun metal, and Ni in monel K and Brightway G. Phosphate, molybdate, tungstate and sulphate were titrated with lead nitrate, with 1,2-naphthoquinone-2-semicarbazone as indicator.hs Aluminium was determined by EDTA back-titration, with 1,2-naphthaquinone-2-thiosemicarbazone-4-sulphonic acid as indicator and zinc solution as titrant.69 Aluminium and copper were determined together by breaking the Al-EDTA complex by addition of sodium fluoride and titrating the released EDTA with zinc.69 Iodide has been determined by mercurimetric titration in isopropyl alcohol, with the same indicator.67 Uses of these compounds as indicators are summarized in Table 3. Applications

as gravimetric reagents

Only a very few semicarbazones and thiosemicarbazones are used in the gravimetric determination of metal ions. Komatsu and Hiroaki used a 0.1% ethanolic solution of p-ethylsulphonylbenzaldehyde thiosemicarbazone for gravimetric determination of Hg 2+ in acidic medium (< 2.5N).49 It gives a yellow precipitate which is washed with IM hydrochloric acid and dried at 110-120”. It is also used for estimation of Pd(IIk5’ giving an orange-yellow precipitate in 5M hydrochloric acid, which is washed with 1:/o hydrochloric acid and water, and dried at 110-120”. Hovorka and Holzbecker’” used salicylaldehyde thiosemicarbazone to precipitate the yellow crystalline Cd(C,H,ON,S), (containing 22.4% Cd) from cadmium nitrate or sulphate solution; the method is not applicable to solutions containing chloride, fluoride or oxalate. 2,4_Dihydroxybenzaldehyde thiosemicarbazone has also been employed for estimation of cadmium44 and nickel.4s In the cadmium estimation at pH 6.5-8.5, Fe3+, A13+, Cr,3i, CN-, citrate, traces of F- and > 2.5 mg/ml of other halides interfere. In the estimation of nickel, green complex the (CsH,N302S),Ni.6H,0 was precipitated in the pH range 5.0-6.5.

2-Furaldehyde thiosemicarbazone has been used by Pavon and Pino(j3 as a gravimetric reagent for palladium at pH 2.0-6.0. The orange precipitate is washed with 10% aqueous ethanol and dried at 60-120”. The reagent is said to have advantages over dimethylglyoxime and 2-furaldioxime. The same authors66 used a 2% ethanolic solution of the 4-phenyl-3-thiosemicarbazone of 2-furaldehyde for gravimetric estimation of palladium in the pH range 3.0-5.0. Potentiometric

studies

Bhatt et aL5’ studied the complexes of 2-hydroxyI-naphthaldehyde-4-phenyl-3-thiosemicarbazone with Cu2+, Ni2+, Co’+ and VO’+ by pH-titration. The proton-ligand stability constant is 1.43 x 10”. The stability constants were determined by several methods in 70% dioxan medium. All four metals formed 1:2 complexes. The order of the stability constants is V02+ > CL?+ rr Co2+ > Ni2 ‘. Complexation by salicylaldehyde-4-phenyl-3-thiosemicarbazone has also been studied potentiometrically by Bhatt et a1.73 at 25” and ionic strength 0.1 in 50% aqueous dioxan. The proton-ligand stability constant is 7.94 x lo9 and the logp values for the complexes are 9.44, 10.28, 9.84 and 8.94 for V02+ Cu2 ‘, Co’+ and Ni2+ respectively. Similar studies were done on the 2-hydroxy-5methylacetophenone thiosemicarbazone complexes33 of Cu(II), Mn(II), Co(II), Zn(I1) and Ni(II), at 40” in water-dioxan (1:3). The order of the stability constants is Zn < Cu > Co > Ni > Mn. Fluorimetric

determination

Salicylaldehyde semicarbazone, 2-hydroxy-l-naphthaldehyde thiosemicarbazone and 2,4-dihydroxybenzaldehyde semicarbazone have also been used for the spectrofluorimetric determination of a number of metal ions, the information for which is summarized in Table 4. Other uses In the presence of cyanide and tartrate, manganese can be detected by a spot-test on paper even when Ag, Pb, Cu, Cd, Bi, Ni, Zn and Fe(II1) are present, by use of an ethanolic solution of dimethylglyoxime 8s Complexes of Cu(II), Hg(II), thiosemicarbazone. Cd(I1) and Zn(I1) with the 4,4’-diphenylthiosemicarbazones of 1,2-diketones can be separated by thin-layer chromatography on alumina with ethyl acetate as solvent.s6 Acknowledgement-One of the authors (RBS) thanks the C.A.S., Delhi University, for awarding him a Teacher Fellowship.

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