Patent Publication Number: US-4221811-A

Title: Antifungal and/or antibacterial organotin compounds, and use

Description:
The present invention relates to antifungal and/or antibacterial organotin compounds, their preparation and use in compositions having high antifungal and antibacterial activities. 
     The great majority of organotin compounds--among which the practically important ones--belong to one of the four classes, tetra-, tri-, di-, and monoorganotin compounds, depending on the number of tin carbon bonds: 
     
         R.sub.4 Sn   R.sub.3 SnY   R.sub.2 SnY.sub.2   RSnY.sub.3 
    
     in which R denotes an organic group bound to tin via carbon, and Y stands for any moiety--organic or inorganic--attached to tin via an electronegative atom, e.g. oxygen, nitrogen, sulphur or simply halogen. 
     It was found in the early 1950&#39;s (see &#34;Organometallic Fungicides&#34;, chapter 7, in &#34;Fungicides, and Advanced Treatise&#34;, vol. II, D. C. Torgeson (ed.), Academic Press, New York, 1969) (1) that many organotin derivatives of the type R 3  SnY are powerful fungicides and bactericides. The nature of the organic group R appeared to be of decisive importance in contrast to the nature of the anionic group Y, which does not appreciably influence the activity. Some dialkyltin derivatives R 2  SnY 2  display interesting antibacterial activity but are inactive against fungi at concentrations ≦500 mg/l. 
     Monoalkyltin compounds RSnY 3  as well as tetraalkyltin compounds R 4  Sn do not display antifungal or antibacterial activity at concentrations ≦500 ppm. 
     In accordance with the above, triorganotin compounds R 3  SnY, have found large-scale practical application as industrial and agricultural fungicides and bactericides, well-known examples being tributyltin derivatives, Bu 3  SnY and triphenyltin derivatives, Ph 3  SnY (see citation (1) and &#34;Technische Herstellung und Verwendung von Organozinnverbindungen&#34;, A. Bokranz and H. Plum, Topics in Current Chemistry, 16(3/4) (1971) 365-403 (3). 
     Until recently very little information was available on functionally substituted alkyltin compounds, i.e. compounds bearing one or more functional groups--such as hydroxyl, amine, carboxyl--on one or more carbon atoms of the hydrocarbon chain. 
     Studies by Noltes, Luijten and Van der Kerk with functionally substituted triorganotin compounds R 3  SnY showed that &#34;the introduction of functional substituents in general reduces antifungal activity&#34; (see citation (1) and &#34;The antifungal properties of some functionally substituted organotin compounds&#34;, J. Appl. Chem., 11 (1961) 38-40 (4). 
     It has now been found that, on the one hand, utilizing newly developed synthetic routes disclosed recently (see W.-German patent application No. 2,228,855 (5) and J. Organomet. Chem. 97 (1975) 167 (6a), J. Organomet. Chem. 117 (1976) 329 (6b)), a series of functionally substituted mono-, di-, tri- and tetra-organotin compounds could be synthesized, in which the introduction of functional groups into fungitoxic triorganotin compounds has the effect of abolishing activity rather than increasing it. 
     On the other hand, it has been found that the introduction of functional groups into hydrocarbon chains can impart high antifungal and/or antibacterial activity to certain classes of organotin compounds. 
     The present invention comprises antifungal and/or antibacterial organotin compounds, which are characterized by the formula 
     
         {R.sub.x.sup.1 R.sub.y.sup.2 R.sub.z.sup.3 Sn[(CH.sub.2).sub.n ].sub.q }.sub.p X.sub.q 
    
     in which R 1 , R 2  and R 3  represent linear or branched alkyl groups having at most 5 carbon atoms or aryl groups, X represents a functional group linked to a carbon atom, x, y, z, n, p and q are integers, n being 1 to 4 inclusive, p being 1 to 3 inclusive, q being 1 or 2 , and if q=2 then x+y+z=2 and p=1 and if q=1 then x+y+z=3. 
     The invention further comprises the preparation of said organotin compounds having the above formula by substituting in a compound having the formula R x   1  R y   2  R z   3  Sn(CH 2 ) n  Br the Br atom by a functional group X. 
     The functional group X is selected from a hydroxyl group, a halogen atom, an ester group, a cyano group, an amino group, an acetamide group, a quaternary ammonium group, a pyridyl group and a piperidine group. Said group X further represents a polyfunctional group such as -NR 4  (CH 2 ) n  NR 5  R 6 , wherein R 4 , R 5  and R 6  represent hydrogen, linear or branched alkyl groups, functionally substituted alkyl groups or aryl groups and n represents an integer of 1 to 4 inclusive. Said polyfunctional group is [the dimethylaminopropyl-] preferably amine moiety -NH(CH 2 ) 3  NMe 2  or complexes thereof with halogen acids, -NH-(CH 2 ) 3  NMe 2 .2HCl or the corresponding quaternary ammonium derivatives, [-NHR(CH 2 ) 3  NMe 2  R] 2+  2 Z - , R being a linear or branched alkyl group and Z being halogen or other suitable anionic groups. 
     The invention further provides antifungal and/or antibacterial compositions, which comprise the above defined organotin compounds, as well as a method for preparing said compositions by combining one or more of the said organotin compounds with a suitable carrier. Said carrier is advantageously a solvent and preferably an aqueous solvent. 
     In the compositions according to the invention also another bactericide or fungicide or insecticide or other active biocidal substances may be taken up. p The invention further provides a process for controlling fungi and/or bacteria, for which purpose one or more of the above defined organotin compounds or compositions respectively are used. 
     Results obtained are compiled in Tables A and B further below. 
     For example, the tetraorganotin compound tripropylethyltin is inactive against fungi and bacteria at concentrations ≦500 mg/l. 
     However, introduction of the 4-pyridyl moiety into the ethyl group imparts high antifungal as well as antibacterial activity to the resulting functionally substituted organotin compound tripropyl-[3-(4-pyridyl)ethyl]tin, Pr 3  SnCH 2  CH 2  ##STR1## This effect is illustrated once more by the high antifungal activity of tributyl-[3-(4-pyridyl)ethyl]tin, Bu 3  SnCH 2  CH 2  ##STR2## As demonstrated by the data obtained for tributyl-(3-carbomethoxyethyl)tin, Bu 3  SnCH 2  CH 2  -COOMe, the introduction of a carboalkoxy group like-wise induces high antifungal and antibacterial activity. The screening data of tributyl(3-bromopropyl)tin, Bu 3  Sn(CH 2 ) 3  Br, and of tributyl(4-bromopropyl)tin, Bu 3  SN(CH 2 ) 4  Br, show that bromine substituents are somewhat less effective, although they show a surprisingly effective antifungal activity. 
     In contrast, the introduction of amino groups and even more so of ammonium moieties can impart strong antifungal and antibacterial activity to tetraorganotin compounds. Thus, tributyl(3-dimethylaminopropyl)tin, Bu 3  Sn(CH 2 ) 3  NMe 2  and tributyl-(4-dimethylaminobutyl)tin, Bu 3  Sn(CH 2 ) 4  NMe 2  display strong antifungal activity at concentrations ≦20 mg/l. Both compounds are also very active against gram-positive bacteria (˜3 mg/l). 
     As mentioned above, according to the literature the introduction of water-solubilizing substituents in triorganotin compounds has a strongly adverse effect on the antimicrobial activity. 
     Other examples of this feature were observed during the studies underlying the present invention. For example, triorganotin compounds such as Bu 3  SnBr, MeBu 2  SnBr, MePrBuSnBr and the like display strong antifungal activity (1), MIC values being about 10 mg/l. However, introduction of a functional group into one of the alkyl groups of such a triorganotin compound has a detrimental effect on the biocidal activity, viz. antifungal activity of MeBuBrSn(CH 2 ) 3  NMe 3  I, MIC &gt;500 mg/l. 
     In contrast, the data presented in Tables A and B show that the introduction of such water-solubilizing functional groups in the case of tetraorganotin compounds strongly promotes both antifungal and antibacterial activity. 
     The nature of the functional substituent is of prime importance with respect to the type of antimicrobial activity induced. For example, introduction of a polyfunctional group such as -NH(CH 2 ) 3  NR 2 , is of particular advantage in that it imparts broad-spectrum activity, that is high biocidal activity against fungi, Gram-positive bacteria and Gram-negative bacteria. 
     Several examples given in Table B demonstrate that in this way organotin chemicals can be obtained, which display high MIC values against Gram-negative bacteria such as E.coli and P.fluorescens (3-10 mg/l). These figures compare very favourably with those of the commercially applied tributyltin biocides (100-500 mg/l). 
     On the basis of the results disclosed in the present invention it can be concluded that those types of organotin compounds that are known to display weak antifungal and antibacterial activity (if any), can be transformed into very active antifungal and antibacterial compounds by incorporating functional substituents, more in particular oxygen and nitrogen containing groups, into the hydrocarbon chain. 
     The compounds may be used as disinfectants, as agricultural and industrial biocides, in antifouling paints, as preservatives for emulsion paints, in wood-preservation, etc. 
     The commercially applied triorganotin biocides have several drawbacks, which are mainly caused by the fact that these compounds are virtually insoluble in water. Therefore, these compounds have to be used in organic solvents, which in many cases is considered to be rather unfavourable because of volatility, inflammability or toxicity of these solvents. More in particular for the application of organotin biocides as preservatives for emulsion paints and in wood-preservation, there is an urgent need for organotin biocides having both a high water-solubility and a broad-spectrum activity. In this respect the quite considerable water-solubility of many of the compounds given in Tables A and B is of particular advantage. 
     For example, the solubility of the commercially applied bis(tributyltin)oxide in water is only 0.003%. In contrast, the solubility in water of Bu 3  Sn(CH 2 ) 3  NMe 2  is about 2%, whereas the solubility of [Me 3  Sn(CH 2 ) 2  ] 2  - ##STR3## (CH 2 ) 3  NMe 2 .2 HCl, MeBu 2  Sn(CH 2 ) 3  NH(CH 2 ) 3  NMe 2 .2HCl, Pr 3  Sn(CH 2 ) 3  NH(CH 2 ) 3  NMe 2 .2HCl and analogous compounds amounts to 50 grams per 100 grams of water, that is 50%. 
     The synthesis of a number of the compounds in question is illustrated in the following Examples. The identity as well as the purity of the compounds obtained were confirmed by H-NMR spectral analysis, for some compounds after methylation of the compound. 
     
                                           Table A                                 
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Antifungal activity of organotin compounds. Minimal concentra-            
tion (mg/l) causing complete inhibition of visible growth (MIC;           
after three days). -Test medium: glucose-agar; pH˜6.9-7.0.          
                           Fungi                                          
                           Botrytis                                       
                                  Penicillium                             
                                         Aspergillus                      
                                                Cladosporium              
Compound                   allii  italicum                                
                                         niger  cucumerinum               
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Bu.sub.4 Sn                &gt;500   &gt;500   &gt;500   &gt;500                      
Bu.sub.3 SnOAc             0.5    0.5    1      1                         
Bu.sub.3 SnCH.sub.2 CN     20     5      1                                
Ph.sub.3 SnCH.sub.2 COOSnPh.sub.3                                         
                           ≦10                                     
                                  ≦10                              
                                         ≦10                       
 ##STR4##                  1      2      5      1                         
 ##STR5##                  2      2      50     ≦1                 
Bu.sub.3 Sn(CH.sub.2).sub.2 CONH.sub.2                                    
                           ≦10                                     
                                  ≦10                              
                                         ≦20                       
                                                ≦10 -Bu.sub.3      
                                                Sn(CH.sub.2).sub.2        
                                                COOMe 0.5 1 5 1           
MeBu.sub.2 Sn(CH.sub.2).sub.3 Br                                          
                           10     &lt;10    100    &lt;10                       
MeBu.sub.2 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2                
                           ≦10                                     
                                  ≦10                              
                                         50     50                        
MeBu.sub.2 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2 . 2            
                           ≦10                                     
                                  ≦10                              
                                         100    20                        
MePh.sub.2 Sn(CH.sub.2).sub.3 NMe.sub.2                                   
                           100    200    500    200                       
MeBuBrSn(CH.sub.2).sub.3 NMe.sub.3 I                                      
                           &gt;500   &gt;500   &gt;500   &gt;500                      
PrSn(CH.sub.2).sub.3 Br    2      5      2      2                         
Pr.sub.3 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2                  
                           ≦10                                     
                                  ≦10                              
                                         10     ≦10                
Pr.sub.3 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2 . 2              
                           ≦10                                     
                                  10     20     20                        
Bu.sub.3 Sn(CH.sub.2).sub.3 Br                                            
                           500    500    500                              
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2                                     
                           10     10     20     20                        
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2 . HCl                               
                           5      5      5      5                         
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.3 I                                   
                           ≦10                                     
                                  50     50     20                        
 ##STR6##                  ≦10                                     
                                  ≦10                              
                                         10     ≦10                
Bu.sub.3 Sn(CH.sub.2).sub.3 OH                                            
                           50     100    100    100                       
Bu.sub.3 Sn(CH.sub.2).sub.3 OCOCH.sub.3                                   
                           50     20     50     20                        
Bu.sub.2 Sn[(CH.sub.2).sub.3 NMe.sub.2 ].sub.2                            
                           50     100    &gt;500   500                       
Bu.sub.2 Sn[(CH.sub.2).sub.3 NMe.sub.3 I].sub.2                           
                           200    200    &gt;500   &gt;500                      
Pent.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.3 I                                 
                           ≦10                                     
                                  20     20     20                        
Ph.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2                                     
                           &lt;10    &lt;10    200    50                        
Ph.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.3 I                                   
                           20     200    &gt;500   500                       
Ph.sub.3 Sn(CH.sub.2).sub.3 NEt.sub.2 MeI                                 
                           50     500    &gt;1000                            
Bu.sub.3 Sn(CH.sub.2).sub.3 NH.sub.2                                      
                                  2      20     5                         
Bu.sub.3 Sn(CH.sub.2).sub.4 Br                                            
                           500    200    200                              
Bu.sub.3 Sn(CH.sub.2).sub.4 NMe.sub.2                                     
                           ≦10                                     
                                  10     ≦10                       
                                                20                        
 ##STR7##                  2      5      10     5                         
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                                           Table B                                 
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Antibacterial activity of organotin compounds. Minimal concentration      
(mg/l)                                                                    
causing complete inhibition of visible growth (MIC; after three days).    
Test medium: peptone-glucose agar; pH ˜ 6.9-7.0.                    
                            Gram-pos. bacteria                            
                                          Gram-neg. bacteria              
Compound                    B. subtilis                                   
                                   S. lactis                              
                                          E. coli                         
                                                 P. fluorescens           
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Bu.sub.4 Sn                 &gt;500   &gt;500   &gt;500   &gt;500                     
Bu.sub.3 SnOAc              2      5      &gt;500   100                      
Pr.sub.3 SnEt               &gt;500   &gt;500   &gt;500   &gt;500                     
 ##STR8##                   10     10     100    100                      
Bu.sub.3 Sn(CH.sub.2).sub.2 CONH.sub.2                                    
                            3      10     &gt;1000  300                      
Bu.sub.3 Sn(CH.sub.2).sub.2 COOMe                                         
                            30     30     100    &gt;1000                    
MeBu.sub.2 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 Nme.sub.2                
                            10     10     10     10                       
MeBu.sub.2 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2 . 2            
                            3Cl    3      3      3                        
MePh.sub.2 Sn(CH.sub.2).sub.3 NMe.sub.2                                   
                            100    100    1000   1000                     
Ph.sub.3 Sn(CH.sub.2).sub.3 Br                                            
                            300    1000   &gt;1000  &gt;1000                    
Pr.sub.3 Sn(CH.sub.2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2                  
                            10     10     10     10                       
Pr.sub.3 Sn(CH.sub. 2).sub.3 NH(CH.sub.2).sub.3 NMe.sub.2 . 2             
                            10l    10     10     10                       
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2                                     
                            3      3      300    1000                     
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2 . HCl                               
                            10     10     300    300                      
Bu.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.3 I                                   
                            ≦1                                     
                                   ≦1                              
                                          30     300                      
 ##STR9##                   30     100    1000   1000                     
Bu.sub.3 Sn(CH.sub.2).sub.3 OH                                            
                            1000   300    &gt;1000  &gt;1000                    
Bu.sub.3 Sn(CH.sub.2).sub.3 OCOCH.sub.3                                   
                            100    100    &gt;1000  300                      
Bu.sub.3 Sn(CH.sub.2).sub.3 Br                                            
                            300    300    &gt;1000  &gt;1000                    
Bu.sub.2 Sn[(CH.sub.2).sub.3 NMe.sub.2 ].sub.2                            
                            100    100    100    300                      
Bu.sub.2 Sn[(CH.sub.2).sub.3 NMe.sub.3 I].sub.2                           
                            300    300    &gt;1000  &gt;1000                    
Ph.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.2                                     
                            10     10     300    &gt;1000                    
Ph.sub.3 Sn(CH.sub.2).sub.3 NMe.sub.3 I                                   
                            10     10     1000   1000                     
Bu.sub.3 Sn(CH.sub.2).sub.4 NH.sub.2                                      
                            3      3      300    300                      
Bu.sub.3 Sn(CH.sub.2).sub.4 NMe.sub.2                                     
                            3      3      &gt;300   &gt;300                     
 ##STR10##                  10     10     30     300                      
__________________________________________________________________________
 
    
     The antifungal and antibacterial compositions according to the present invention may contain another bactericide or fungicide or insecticide or other active biocidal substances. 
    
    
     EXAMPLE I 
     (A) The preparation of Br 3  Sn(CH 2 ) n  Br (n=3-4) 
     A mixture of 111.6 g (0.40 mol) of anhydrous SnBr 2 ,363 g (1.80 mol) of Br(CH 2 ) 3  Br and 4 ml (5.25 g, 0.025 mol) of Et 3  Sb was stirred for 4.5 h at 150°-160° C. The SnBr 2  had been completely converted. Evaporation in vacuo (14 mm Hg) at 100° C. gave 272 g (1.35 mol) of recovered Br(CH 2 ) 3  Br, leaving 206 g of a brown, oily liquid. Distillation in vacuo (mercury diffusion pump) gave 141.6 g (74%) of pure Br 3  Sn(CH 2 ) 3  Br. 
     In a similar way Br 3  Sn(CH 2 ) 4  Br was prepared. 
     (B) The preparation of R 3  Sn(CH 2 ) n  Br (n=3-4) 
     A solution of 20 g (0.042 mol) of Br 3  Sn(CH 2 ) 3  Br in 100 ml of diethyl ether was added drop-wise to 80 ml of a 2.5 N solution of MeMgBr in diethyl ether. After reflux for 2 h the mixture was treated with a saturated aqueous solution of NH 4  Cl and distilled to give 8.7 g (74%) of (3-bromopropyl)trimethyltin. 
     In a similar way were prepared: (3-bromopropyl)tripropyltin, (3-bromopropyl)tributyltin, (3-bromopropyl)tripentyltin and (3-bromopropyl)triphenyltin, (4-bromobutyl)tributyltin and related compounds. 
     (C) The preparation of R x   1  R y   2  R z   3  Sn(CH 2 ) n  Br (n=3, 4) 
     Over a period of 1.5 hour 140 g (0.874 mol) of bromine was added to a solution of 125 g (0.437 mol) of Me 3  Sn(CH 2 ) 3  Br in 450 ml of methanol kept at -20° C. The mixture was stirred at room temperature till the orange-red colour had changed into slightly yellow. Evaporation of the solvent in vacuo gave 174 g (96%) of (3-bromopropyl) methyltin dibromide, n D   20  =1.6215. 
     A solution of 115 ml of 2.7 N butylmagnesium bromide in diethyl ether was added in about one hour to a solution of 62.5 g (0.15 mol) of (3-bromopropyl)methyltin dibromide in 200 ml of diethyl ether. After reflux for 1 h the mixture was treated with a saturated aqueous solution of NH 4  Cl and distilled to give 48.79 g (88%) of (3-bromopropyl)methyldibutyltin; b.p. 88°-90° C./0.1 mm Hg, n D   20  =1.5001. 
     In a similar way were prepared (3-bromopropyl)methyldiphenyltin and related compounds. 
     EXAMPLE II 
     The preparation of Bu 3  Sn(CH 2 ) 3  NMe 2  and related compounds 
     In a reaction vessel provided with a carbon dioxide condenser, a mixture of 6.18 g (0.015 mol) of Bu 3  Sn(CH 2 ) 3  Br and 20 ml of Me 2  NH was refluxed for 7 h. The residue obtained after evaporation of the excess of Me 2  NH was taken up in 30 ml of diethyl ether and treated for 15 min with 50 ml of a 10% aqueous solution of NaHCO 3 . Distillation gave 4.95 g (86%) of (3-dimethylaminopropyl)tributyltin. 
     Analogously were prepared: (3-dimethylaminopropyl) methyldiphenyltin, (3-dimethylaminopropyl)trimethyltin, (3-dimethylaminopropyl)triphenyltin, (4-dimethylaminobutyl)tributyltin and related compounds. 
     EXAMPLE III 
     The preparation of N-[3-(tripropylstannyl)propyl-N&#39;, N&#39;-dimethyltrimethylene]diamine, Pr 3  Sn(CH 2 ) 3  NH(CH 2 ) 3  NMe 2   
     Over a period of 0.5 hour 9.25 g (0.025 mol) of (3-bromopropyl) tripropyltin was added to 25 ml of 3-dimethylaminopropyl amine at room temperature. The mixture was stirred for 1 hour at 60° C. Under cooling 75 ml of diethylether and 60 ml of a 15% aqueous solution of sodium bicarbonate were added. After stirring for 0.5 hour the organic phase was separated, dried and evaporated in vacuo. Distillation gave 7.5 g (77%) of Pr 3  Sn(CH 2 ) 3  NH(CH 2 ) 3  NMe 2  ; b.p. 113°-114° C./0.1 mm Hg, n D   20  =1.4855. 
     In a similar way were prepared N-[3-(methyldibutylstannyl) propyl-N&#39;, N&#39;-dimethyltrimethylene]diamine, MeBu 2  Sn(CH 2 ) 3  NH(CH 2 ) 3  NMe 2 , {Bu 3  Sn(CH 2 ) 3  NH(CH 2 ) 3  N[(CH 2 ) 3  SnBu 3  ]CH 2  } 2  and related compounds. 
     By conventional techniques the products can be readily converted into the corresponding halogen acid salts, quaternary ammonium derivatives, and the like. 
     EXAMPLE IV 
     Bis(trimethylammoniopropyl)dibutyltin diiodide, Bu 2  Sn[(CH 2 ) 3  NMe 3  I] 2   
     A solution of 22.8 g (0.075 mol) of Bu 2  SnCl 2  in 80 ml of benzene was added slowly at 0° C. to 70 ml of a TMF solution containing 0.18 mol of (3-dimethylaminopropyl)magnesium chloride. The resulting mixture was diluted with 100 ml of diethyl ether and refluxed for 2 hours. After the usual work-up the product was distilled to give 28.1 g (92.5%) of Bu 2  Sn[(CH 2 ) 3  NMe 2  ] 2  ; b.p. 112°-114° C./0.0 mm Hg, n D   20  =1.4829. 
     To a solution of 6.1 g (0.015 mol) of Bu 2  Sn[(CH 2 ) 3  NMe 2  ] 2  in 50 ml of methanol was added slowly 4.26 g (0.03 mol) of methyl iodide. Evaporation in vacuo gave 10.2 g (97%) of solid Bu 2  Sn[(CH 2 ) 3  NMe 3  I] 2  ; m.p. 194°-195° C.