3542-36-7

Basic information

• Product Name: DI-N-OCTYLTIN DICHLORIDE
• Synonyms: dichlorodioctyl-stannan;dichlorodioctylstannane;dichlorodioctyl-Stannane;di-n-octyl-zinndichlorid;dioctyldichloro-stannan;dioctyldichlorotin95%;dioctylstanniumdichloride;dioctyl-tidichloride
• CAS NO: 3542-36-7
• Molecular Formula: C₁₆H₃₄Cl₂Sn
• Molecular Weight: 416.06
• EINECS: 222-583-2
• Mol File: 3542-36-7.mol
• Article Data: 4

Chemical Properties

• Melting Point: 46-48°C
• Boiling Point: 175°C 1mm
• Flash Point: 204°C
• Appearance: /solid
• Density: 1,175 g/cm3
• Vapor Pressure: 7.38E-06mmHg at 25°C
• Water Solubility: Insoluble in water.
• Sensitive: Moisture Sensitive
• CAS DataBase Reference: DI-N-OCTYLTIN DICHLORIDE(CAS DataBase Reference)
• NIST Chemistry Reference: DI-N-OCTYLTIN DICHLORIDE(3542-36-7)
• EPA Substance Registry System: DI-N-OCTYLTIN DICHLORIDE(3542-36-7)

Safety Data

• Statements: 36/37/38-48/20/22
• Safety Statements: 26-35-36/37/39
• RIDADR: 3146
• RTECS: WH7247000
• TSCA: Yes
• HazardClass: 6.1
• PackingGroup: II
• Hazardous Substances Data: 3542-36-7(Hazardous Substances Data)

Usage

Description

DI-N-OCTYLTIN DICHLORIDE is an organotin compound that serves as an intermediate in the production of various organotin chemicals, including Metatin and Acima. It is characterized by its ability to act as a catalyst or industrial intermediate in the synthesis of different materials.

Uses

Used in Chemical Production:
DI-N-OCTYLTIN DICHLORIDE is used as an intermediate for the production of other organotin chemicals, such as Metatin and Acima. Its role in the synthesis process is crucial for the development of these compounds.
Used in Catalysts and Industrial Intermediates:
DI-N-OCTYLTIN DICHLORIDE is utilized as a catalyst or industrial intermediate in the production of various materials, including polyurethanes, silicone resins, synthetic lubricants, and MS polymer sealants. Its presence in these processes aids in enhancing the properties and performance of the final products.
Used in the Plastics Industry:
In the plastics industry, DI-N-OCTYLTIN DICHLORIDE is used as a catalyst for the production of polyurethanes. Its catalytic properties contribute to the formation of polyurethanes with desired characteristics, such as flexibility, durability, and resistance to various environmental factors.
Used in the Silicone Industry:
DI-N-OCTYLTIN DICHLORIDE is employed as an intermediate in the synthesis of silicone resins. Its involvement in the production process helps create silicone resins with improved properties, such as thermal stability, electrical insulation, and resistance to extreme temperatures.
Used in the Lubricants Industry:
In the lubricants industry, DI-N-OCTYLTIN DICHLORIDE is used as an intermediate for the production of synthetic lubricants. Its presence in the manufacturing process contributes to the development of lubricants with enhanced performance, such as reduced friction, wear resistance, and improved thermal stability.
Used in the Sealants Industry:
DI-N-OCTYLTIN DICHLORIDE is utilized as an intermediate in the production of MS polymer sealants. Its role in the synthesis process helps create sealants with superior properties, such as high adhesion, flexibility, and resistance to various environmental conditions.

InChI:InChI=1/2C8H17.2ClH.Sn/c2*1-3-5-7-8-6-4-2;;;/h2*1,3-8H2,2H3;2*1H;/q;;;;+2/p-2/rC16H34Cl2Sn/c1-3-5-7-9-11-13-15-19(17,18)16-14-12-10-8-6-4-2/h3-16H2,1-2H3

Synthetic route

trioctylaluminum (1070-00-4) → n-octyltin trichloride (3091-25-6) + di-n-octyltin dichloride (3542-36-7) + trioctyltin chloride (2587-76-0)

Conditions	Yield
With tert-butyl methyl ether; tin(IV) chloride at 50℃; for 0.75h; Product distribution / selectivity;	A 98% B 98% C 98%
With 1,3-dioxane; tin(IV) chloride at 50℃; for 0.75h; Product distribution / selectivity;	A 97.3% B 97.3% C 97.3%
With diethyl ether; tin(IV) chloride at 50℃; for 0.75h; Product distribution / selectivity;	A 96.8% B 96.8% C 96.8%
With tetrahydrofuran; tin(IV) chloride at 50℃; for 0.75h; Product distribution / selectivity;	A 95.6% B 95.6% C 95.6%
With dibutyl ether; tin(IV) chloride at 50 - 100℃; for 0.75h; Product distribution / selectivity;	A 89% B 89% C 89%

tin (7440-31-5) + 1-Chlorooctane (111-85-3) → di-n-octyltin dichloride (3542-36-7) + trioctyltin chloride (2587-76-0)

Conditions	Yield
With catalyst: dibenzo-18-crown-6 In N,N-dimethyl-formamide 160°C; excess KI;; analyzed by GLC;;	A 95% B 5%
With catalyst: {(n-C4H9)4N}I/n-C8H17I analyzed by GLC;;	A 70% B 30%

1-Chlorooctane (111-85-3) + tin(IV) chloride (7646-78-8) → tetraoctyltin (3590-84-9) + di-n-octyltin dichloride (3542-36-7) + trioctyltin chloride (2587-76-0)

Conditions	Yield
With sodium In Petroleum ether (Ar); vigorous stirred suspn. of Na was maintained at 115°C for 0.5 h, one drop of SnCl4 was added and ClC4H9 was added dropwise within 3 h at 30-40°C, after 1 h stirring SnCl4 (4:1 mol) was dropped into mixt. (same temp.) within 75 min; after stirring for a further h at 30-40°C mixt. was filtered off and residue treated with tBuOH, solvents were distd. off from filtrate; identification by GC after methylation;	A 54.3% B 3.7% C 15.2%
With sodium In Petroleum ether (Ar); vigorous stirred suspn. of Na was maintained at 115°C for 0.5 h, one drop of SnCl4 was added and ClC4H9 was added dropwise within 3 h at 40°C, mixt. was added portionswise to soln. of SnCl4 (2:1 mol) over 2 h at 20-40°C; mixt. was filtered off and residue treated with tBuOH, solvents were distd. off from filtrate; identification by GC after methylation;	A 14% B 22% C 46%

Schwartz's reagent + oct-1-ene (111-66-0) + tin(IV) chloride (7646-78-8) → zirconocene dichloride (1291-32-3) + n-octyltin trichloride (3091-25-6) + di-n-octyltin dichloride (3542-36-7)

Conditions

Yield

In hexane; benzene a mixt. of Cp2ZrHCl and 1-octene in benzene was stirred for ca. 2 h at room temp. under N2, a soln. of anhyd. SnCl4 in n-hexane was added dropwise (Cp2ZrHCl/SnCl4 ratio 4:1), stirred for a further 1 h 30 min; hexane was added, ppt. of Cp2ZrCl2 was filtered off, filtrate concd., residue extd. with hexane, exts. concd., dild. with methanol; (octyl)SnCl3 content was detd. by titrn. with EDTA, yield of (octyl)2SnCl2 was estimated by conversion into (octyl)2SnO;

A n/a B 35% C 35%

oct-1-ene (111-66-0) + n-octyltin trichloride (3091-25-6) → di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
With (η5-C5H5)2Zr(H)Cl In hexane; benzene mixt. of Cp2ZrHCl and 1-octene in benzene was stirred for ca. 2 h at room temp. under nitrogen, hexane soln. of (n-octyl)SnCl3 was added, mixt. was refluxed in the presence of added solvents such as n-Bu2O and DMF;	0%

n-octylzirconocene chloride + n-octyltin trichloride (3091-25-6) → di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
With copper(l) iodide In sulfolane stoich. amount of CuI. 0°C;	0%

tetraoctyltin (3590-84-9) → octylmercury (1+); chloride (26674-66-8) + di-n-octyltin dichloride (3542-36-7) + trioctyltin chloride (2587-76-0)

Conditions	Yield
With mercury dichloride In ethanol boiling ethanol;;
With HgCl2 In ethanol boiling ethanol;;

tetraoctyltin (3590-84-9) → di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
With mercury dichloride In ethanol reflux;
With HgCl2 In ethanol reflux;

boron trichloride (10294-34-5) + tetraoctyltin (3590-84-9) → (n-octyl)dichloroborane (63348-82-3) + di-n-octyltin dichloride (3542-36-7) + tin(ll) chloride

Conditions	Yield
In acetone molar ratio 1:2, under CO2 atmosphere;

tin(IV) chloride (7646-78-8) + tetraoctyltin (3590-84-9) → n-octyltin trichloride (3091-25-6) + di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
240°C;
240°C;
240°C;

tetraoctyltin (3590-84-9) + tin(ll) chloride → di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
With AlCl3 130°C;
With aluminium trichloride 130°C;

diethyldioctylstannate (14775-13-4) → (C8H17)2CH3CH2SnCl (75006-32-5) + ethylmercury(II) chloride (107-27-7) + di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
With mercury dichloride In ethanol boiling ethanol;;
With HgCl2 In ethanol boiling ethanol;;

dimethyl-dioctyl stannane (40218-15-3) + tin(IV) chloride (7646-78-8) → dimethyltin dichloride (753-73-1) + di-n-octyltin dichloride (3542-36-7)

trioctylaluminum (1070-00-4) → n-octyltin trichloride (3091-25-6) + di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
Multi-step reaction with 2 steps 1: 2,2,4-trimethylpentane View Scheme

trioctylaluminum (1070-00-4) → di-n-octyltin dichloride (3542-36-7)

Conditions	Yield
Multi-step reaction with 2 steps 1: 2,2,4-trimethylpentane 2: AlCl3 View Scheme
Multi-step reaction with 2 steps 1: 2,2,4-trimethylpentane 2: HgCl2 / ethanol View Scheme

1-Chlorooctane (111-85-3) + di-n-octyltin dichloride (3542-36-7) → tetraoctyltin (3590-84-9)

Conditions	Yield
With Na	98%
With sodium	98%

methylmagnesium chloride (676-58-4) + di-n-octyltin dichloride (3542-36-7) → dimethyl-dioctyl stannane (40218-15-3)

Conditions	Yield
In diethyl ether	97%
In diethyl ether	97%

di-n-octyltin dichloride (3542-36-7) + Dimethyl phosphite (868-85-9) → dioctylstannyl bis(O-methylphosphonate)

Conditions	Yield
In neat (no solvent) byproducts: CH3Cl; heating to 120°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	94%
zinc(II) chloride In dimethyl sulfoxide; chlorobenzene byproducts: CH3Cl; addn. of ZnCl2 to Sn-compd. and phosphonate in chlorobenzene/DMSO, heating to 120-140°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	94%
In water byproducts: CH3Cl; heating to 90°C (4 h); pptn. by cooling;	94%

pyridine N-oxide (694-59-7) + di-n-octyltin dichloride (3542-36-7) → (C8H17)2SnCl2(C5H5NO)2

Conditions	Yield
In chloroform Sn-compd. added to soln. of ligand, refluxed on a water-bath for about 2h; solvent removed under reduced pressure, crystd. from EtOH; elem. anal.;	92%

di-n-octyltin dichloride (3542-36-7) + phosphonic acid diethyl ester (762-04-9) → dioctylstannyl bis(O-ethylphosphonate)

Conditions	Yield
zinc(II) chloride In dimethyl sulfoxide; chlorobenzene byproducts: C2H5Cl; addn. of ZnCl2 to Sn-compd. and phosphonate in chlorobenzene/DMSO, heating to 120-140°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	91%
In water byproducts: C2H5Cl; heating to 90°C (4 h); pptn. by cooling;	91%
In neat (no solvent) byproducts: C2H5Cl; heating to 120°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	91%

2Ag(1+)*(OOCCH2)2HNCH2CH2NH(CH2COO)2(2-)=(OOCCH2)2HNCH2CH2NH(CH2COO)2Ag2 + di-n-octyltin dichloride (3542-36-7) → (C8H17)2Sn((CH2NH(CH2COO)2)2) (144910-02-1) + silver(I) chloride

Conditions	Yield
In ethanol addn. of Sn-compd. soln. to EDTA salt soln. (molar ratio 1:1), refluxing (water bath, 4 h); filtration, washing (ethanol), filtrate distn., drying (vac.), recrystn. (ethanol); elem. anal.;	A 89% B n/a

diisopropyl hydrogenphosphonate (1809-20-7) + di-n-octyltin dichloride (3542-36-7) → dioctylstannyl bis(O-isopropylphosphonate)

Conditions	Yield
zinc(II) chloride In dimethyl sulfoxide; chlorobenzene byproducts: (i-Pr)Cl; addn. of ZnCl2 to Sn-compd. and phosphonate in chlorobenzene/DMSO, heating to 120-140°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	88%
In water byproducts: (i-Pr)F; heating to 90°C (4 h); pptn. by cooling;	88%
In neat (no solvent) byproducts: (i-Pr)Cl; heating to 120°C (4 h); distn. in vac., mixing residue (ether or MeOH/H2O 1:1), filtration, drying in vac.; elem. anal.;	88%

2,2',2''-triaminotriethylamine (4097-89-6) + 5-methyl-4-formylimidazole (68282-53-1) + di-n-octyltin dichloride (3542-36-7) → fac-cis-[di-n-octyltin(IV)(tren(4-Me-5-ImH)3(-2H))]

Conditions	Yield
In methanol mixt. of 4-Me-5-ImH (4.5 mmol) and tren (1.5 mmol) in MeOH stirred underN2 and refluxed for 1 h, cooled to room temp., hot n-Oct2SnCl2 (1.5 mmo l) soln. added with stirring, heated with stirring for 48 h at 60-65°C; filtered, excess of solvent removed under vac., solid recrystd. from CH2Cl2/MeOH (2:1 v/v); elem. anal.;	88%

ammonium saccharin (6381-61-9) + di-n-octyltin dichloride (3542-36-7) → (CH3(CH2)7)2Sn(NCOSO2C6H4)2 (91375-23-4)

Conditions	Yield
In methanol byproducts: ammonium chloride; ammonium saccharin was added to a soln. of n-Oct2SnCl2 in anhyd. methanol, mixt. was refluxed for 1 h; filtered, filtrate evapd. in vacuo, NH4Cl was removed by washing several times with distilled water, recrystd. twice from methanol; elem. anal.;	85%

ammonium dimolybdate + di-n-octyltin dichloride (3542-36-7) → (C8H17)2SnMoO4

Conditions	Yield
In methanol; water a soln. of molybdate in warm aq. MeOH was added to a MeOH soln. of stannane, a white ppt. formed rapidly;; ppt. filtered, washed with water and dried in air; elem. anal.;	82%

2-methylpyridine N-oxide (931-19-1) + di-n-octyltin dichloride (3542-36-7) → (C8H17)2SnCl2(C5H4(CH3)NO)2

Conditions	Yield
In chloroform Sn-compd. added to soln. of ligand, refluxed on a water-bath for about 2h; solvent removed under reduced pressure, crystd. from CHCl3; elem. anal.;	80%

di-n-octyltin dichloride (3542-36-7) + Natriumsalz des Thiophosphorsaeure-O,O-dimethylesters (23754-87-2) → bis(O,O'-dimethylmonothiophosphato)di-n-octyltin(IV) (85913-93-5)

Conditions	Yield
In ethanol byproducts: NaCl; 1 h, reflux; filtration, washing with distilled water, elem. anal.;	80%

N-(p-bromophenyl)maleamic acid (59256-47-2) + di-n-octyltin dichloride (3542-36-7) → Sn(C8H17)2(C6H4BrNHC(O)CHCHCOO)2

Conditions	Yield
With triethylamine In toluene byproducts: N(C2H5)3*HCl; 4-bromomaleanilic acid and triethylamine added to toluene, refluxed for 2-3 h, organotin compound added under stirring, mixt. refluxed for 8-10 h; N(C2H5)3*HCl filtered off, solvent removed (vac.), solid recrystd. (CHCl3/n-C6H14); elem. anal.;	80%

3Ag(1+)*(OOCCH2)2NCH2CH2NH(CH2COO)2(3-)=(OOCCH2)2NCH2CH2NH(CH2COO)2Ag3 + di-n-octyltin dichloride (3542-36-7) → ((C8H17)2Sn)3((OOCCH2)2NCH2CH2NH(CH2COO)2)2 (144910-03-2) + silver(I) chloride

Conditions	Yield
In ethanol addn. of Sn-compd. soln. to EDTA salt soln. (molar ratio 3:2), refluxing (water bath, 4 h); filtration, washing (ethanol), filtrate distn., drying (vac.), recrystn. (ethanol); elem. anal.;	A 76% B n/a

1,4-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)butane-1,4-dione (112525-81-2) + di-n-octyltin dichloride (3542-36-7) → bis[(1,4-bis(5-hydroxy-1-phenyl-3-methyl-1H-pyrazol-4-yl)butane-1,4-dionate)dioctyltin(IV)]

Conditions	Yield
With KOH In methanol byproducts: H2O, KCl; (N2); stirred overnight; ppt. filtered off, washed (MeOH), recrystd. (CHCl3/MeOH); elem. anal.;	75%

sodium 2-(4-methoxy-2-nitrophenylcarbamoyl)benzoate + di-n-octyltin dichloride (3542-36-7) → dioctylstannanediyl bis 2-(4-methoxy-2-nitrophenylcarbamoyl)benzoate

Conditions	Yield
In toluene for 8h; Reflux;	75%

C11H12NO4(1-)*Na(1+) + di-n-octyltin dichloride (3542-36-7) → dioctylstannanediyl bis(4-(2-methoxyphenylamino)-4-oxobutanoate)

Conditions	Yield
In toluene for 8h; Reflux;	73%

disodium piperazinobis(dithiocarbamate) dihydrate + di-n-octyltin dichloride (3542-36-7) → dioctylstannylpiperazine bis(dithiocarbamate)

Conditions	Yield
In ethanol byproducts: NaCl; elem. anal., IR-, Moessbauer spectroscopy;;	72%

ammonium N-pyrrolidinyldithiocarbamate + di-n-octyltin dichloride (3542-36-7) → bis(tetramethylenedithiocarbamato)di-n-octyltin(IV) (73160-43-7)

Conditions	Yield
In methanol byproducts: ammonium chloride; n-Oct2SnCl2 was added to a methanol soln. of (CH2)4NS2NH4, mixt. was refluxed for 3 h; ppt. was removed by filtration, excess solvent removed under reduced pressure; elem. anal.;	72%

N'1,N'4-bis(2-hydroxybenzylidene)succinohydrazide (64174-57-8) + di-n-octyltin dichloride (3542-36-7) → bis[di(n-octyl)tin(IV)] [N'1,N'4-bis(2-hydroxybenzylidene)succinohydrazide]

Conditions	Yield
In toluene Reflux;	72%

S-benzyl-β-N-(2-hydroxy-1-naphthyl)methylendithiocarbazate, disodium + di-n-octyltin dichloride (3542-36-7) → (C8H17)2Sn(SBND)

Conditions	Yield
In benzene addn. of Sn-salt to suspn. (benzene) of disodium-salt of ligand, refluxing (5 h); elem. anal.;	70%

S-benzyl-β-N-(2-hydroxy-3-methoxyphenyl)methylendithiocarbazate, disodium + di-n-octyltin dichloride (3542-36-7) → (C8H17)2Sn(SBVD)

Conditions	Yield
In benzene addn. of Sn-salt to susp. (benzene) of disodium-salt of ligand, refluxing (5 h); elem. anal.;	68%

EDTA silver salt + di-n-octyltin dichloride (3542-36-7) → ((C8H17)2Sn)2((CH2N(CH2COO)2)2) (144889-85-0) + silver(I) chloride

Conditions	Yield
In ethanol addn. of Sn-compd. soln. to EDTA salt soln. (molar ratio 2:1), refluxing (water bath, 4 h); filtration, washing (ethanol), filtrate distn., drying (vac.), recrystn. (ethanol); elem. anal.;	A 65% B n/a

cupferron + di-n-octyltin dichloride (3542-36-7) → Oc2Sn(N-nitroso-N-phenylhydroxylaminate)2 (947265-19-2)

Conditions	Yield
In methanol byproducts: NH4Cl; ligand and Sn-complex dissolved in MeOH, stirred and refluxed; soln. kept in refrigerator, filtered, crystd., recrystd. from hexane or MeOH; elem. anal.;	64%

di-n-octyltin dichloride (3542-36-7) + Cyclohexanecarboxylic acid (98-89-5) → [Oct4Sn2(C6H11COO)(μ3-O)(μ-OH)]2

Conditions	Yield
With potassium hydroxide In methanol; water at 20℃;	55%

lithium aluminium tetrahydride (16853-85-3) + di-n-octyltin dichloride (3542-36-7) → dioctylstannane (15231-44-4)

Conditions	Yield
In diethyl ether boiling on reflux for 2.5 h;;	45%
In diethyl ether boiling on reflux for 2.5 h;;	45%

2-Methylthiophene (554-14-3) + di-n-octyltin dichloride (3542-36-7) → bis(5-methyl-2-thienyl)dioctyltin(IV) (117013-16-8)

Conditions	Yield
With n-C4H9Li In not given stirring (4 h, room temp.);	40%

Upstream product

• 111-66-0 oct-1-ene 
• 3091-25-6 n-octyltin trichloride 
• 1070-00-4 trioctylaluminum 
• 40218-15-3 dimethyl-dioctyl stannane 
• 7646-78-8 tin(IV) chloride 
• 14775-13-4 diethyldioctylstannate 
• 3590-84-9 tetraoctyltin 
• 10294-34-5 boron trichloride 
• 111-85-3 n-chlorooctane 
• 7440-31-5 tin 

Downstream Products

• 3590-84-9 tetraoctyltin 
• 2787-93-1 bis(trioctylstannyl) oxide 
• 2587-76-0 trioctyltin chloride 
• 947265-19-2 Oc₂Sn(N-nitroso-N-phenylhydroxylaminate)2 
• 79138-57-1 ((C₆H₅)2PO(CH₂)4P(C₆H₅)2O)(C₈H₁₇)2SnCl₂ 
• 80243-62-5 bis(phenyl phenylphosphonato)di-n-octyltin(IV) 
• 79138-56-0 ((C₆H₅)2PO(CH₂)2P(C₆H₅)2O)(C₈H₁₇)2SnCl₂ 
• 40218-15-3 dimethyl-dioctyl stannane 
• 15231-44-4 Di-n-octylstannan 

Relevant articles and documents

Process for the preparation of mono- and dialkyltin halogen compounds and use thereof

Production of mixtures of monoalkyl tin trichlorides (I) and dialkyl tin dichlorides (II) by reacting tin tetrachloride with an alkyl aluminum compound in the form of an ether donor complex comprises using an amount of ether in excess of that required to form the complex. Independent claims are also included for: (1) mixtures of (I) and (II) produced as above in a yield of at least 90 mole% based on tin tetrachloride; (2) mixtures of (I) and (II) comprising at least 50 mole% (I); (3) mixtures of (I) and (II) comprising up to 5 mole% trialkyl tin chlorides; (4) mixtures of (I) and (II) comprising at least 50 mole% (I), at least 20 mole% (II) and up to 5 mole% trialkyl tin chloride.

A highly selective synthesis of R2SnX2 (R = alkyl, X = Br, Cl) species directly from tin and alkyl halides

The reaction : Sn + 2RX -> SnR2X2 (X = Cl, Br) occurs at relatively low temperature (80 - 120 degC) and with selectives as high as 95 - 99percent in the presence of catalytic system fored by a crown ether and potassium iodide.The reaction is favoured by aprotic dipolar solvents such as dimethylformamide; the presence of an alkyl iodide as cocatalyst has a positive effect, the selectivity remaining unchanged.