INTRODUCTION:

Organoselenium ligands are chemical compound containing carbon to selenium chemical bonds. Organoselenium chemistry is the corresponding science exploring their property and reactivity^(1-4).The selenium metal belongs to the oxygen family(group 16).selenium can exist in oxidation state -2, +2, +4, +6 but most common+2, down the group (group 16)bond strength become weaker (234kJ/mol for the C-Se bond and 272 kJ/mol for C-S bond and the bond length longer (C-Se 198pm, than C-S 182pm and C-O 141 pm). Over 30 years Organoselenium Chemistry has been the subject of constant scientific interest and now is very useful tool in the hands of synthetic chemists^5.Organic selenides are key intermediates in organic synthesis as well as in medicine⁶. Two most important classes of organoselenium compound are selenide, diselenides.

These organoselenium acts as both electrophile and nucleophile but we have used here as nucleophile, so with help of neucleophilic displacement reaction we have made many selenide like methyl benzyl selenide, dihexyl selenide and diselenide like 1,1ethylidene diselenide, dibutyldiselenide organoselenium compound which have shown in table. These made organoselenium ligand have antioxidant, apoptosis antiviral, antifungal, antihistamine and antitumer properties.⁷ These selenium ion are formed from element selenium reaction with reductants that we have used such as NaBH₄⁸, NaH⁹, Na¹⁰ or organic lithium to prepare selenide. Recently, an effective methods have been used to synthesized unsymmetrical selenide that is organic halide with the help of reduction form product. Different type of catalyst like indium, copper, palladium, tin, nickel are also used to prepare organoselenium ligand or compound. These made organoselenium compound can also be used in nature that is an essential micronutrients whose absence from the diet cause cardiac muscle and skeletal dysfunction. These Organoselenium compound are required for cellular defense against oxidative damage and for correct functioning of immune system. They may also play a role in prevention of premature aging and cancer.

EXPERIMENTAL PROCESS:

Generally - In this process first of all, 1equi.of grey powder selenium Mixed with commercially available 2.0 equi. of Li(C₂H₅)₃BH in THF(1.0M THF sold as superhydride) under dry N₂ with stirring in gas evolution stirring continued for at least 20 minute so that reaction mixture become milky white at this point Li₂Se is formed, after addition of THF, solution of alkyl halide (2equiv) to the mix with Li₂Se, R₂Se₂ slightly yields are obtained however better resulted when some t-butyl alcohol (1.5-5.equiv) was added with help of alkyl halide as a solvent. In this reaction, reaction time depends upon reactivity of alkyl halide, more the reactivity of alkyl halide more will faster the reaction, after ether extraction washing and drying takes place, so that by product triethyl-borane are removed by solvent evaporation. Yields (Shown in table 2) obtained by reference to ¹H NMR internal standard, IR or the product obtained column chromatography. NMR, IR, Elemental analysis, yields are shown in respective table.

Preparation of Lithium Selenide suspension in THF:

Grey selenium (0.22 gm, 2.75 mmol) added portionwise 5.75 mL of Li(C₂H₅)₃BH solution (5.70mmol)with help of magnetic stirring. Gas evolution occurred and ceased within 20 minute the solution turned into heterogeneous milky white. THF(3mL)added and the allowed to stirring 20 minute.

Preparation of alkyl selenide product:

1.Dimethyl benzyl selenide:

Benzyl bromide 0.65mL (6.00mmol)in 4.5 mL of THF added dropwise to Li₂Se (2.90mmol)suspended in 0.5 mL (4.5mmol)of tert-butyl alcohol and 10 mL of THF. After addition was completed, the reaction mixture stirred overnight and give the result.

2.Di-n-butyl, diselenide:

Solution of 1bromobutane 0.70 mL(5.80mmol) and tert-butyl alcohol0.45mL(5.2mmol)in 4.5 mL of THF added overnight to Li₂Se₂ (2.75mmol)suspended in 8 mL of THF when reaction completed describe the result(NMR, IR, data etc).

REACTION

Se +2Li(C₂H₅)₃BH →Li₂Se + 2(C₂H₅)₃B + H₂1(a)

R=1, 2 (TABLE2) Li₂Se + 2RX →R₂Se 1(b)

R=3, 4(TABLE) 2Se + 2LI(C₂H₅)₃BH → Li₂Se₂ + 2(C₂H5)₃B +H₂1(c)

Li₂Se₂+ 2RX→R₂Se_{2 1(d)}

Table(1) NMR, IR

R	NMR	IR
1.Di -n –Butyl di selenide	Chemical Shift 2.57 (t, j=7.5 Hz, 4H, SeCH₂₎), 1.68-1.60 (m, 4H, CH₂CH₂), 1.45-1.38(m, 4H, CH₂CH₃), 93(t, j=7.4Hz, 6H, CH₃)	Vmax/cm^-2958, 2928, 2870, 1460, 1376, 1256, 1193, 736 cm^-1
2.Di Methyl benzyl Selenide	Chemical Shift 7.26-7.12(m, 8H, ArH), 3.74(S, 4H, CH₂), 2.38(S, 6H, CH₃)	Vmax-/v cm^-1-3020, 2919, 1511, 1415, 1179, 1020, 817, 715, Cm^-1
3.Di-cyclohexyl selenide	Chemical shift 3.0-2.93(m, 2H CHSe), 2.30-1, 99(m, 8H, CH₂CHSe), 1.76-1.34(m, 12H, CH₂)	V max/Cm^-12880, 1453, 1350, 1258, 997, 889, Cm^-1
4.Di-1,1–Ethylidenedi selenide	Chemical Shift 7.35-7.31(m, 10H, Ar-H)4.09 -3.92(m, 2H, CHCH₃), 179-1.65(m, 6H, CHCH₃)	Vmax/VCm^-13026, 2959, 2862, 1600, 1492, 1452, 1372, 1083, 1023, 762, 696 Cm^-1

Table2. Dialkyl selenide and Dialkyl Diselenide prepared

R	Yield%(1, 2 are selenide, 3.4 are diselenide)
1.Methyl benzyl	85
2.Cyclohexyl	58
3.n-Butyl	48
4.1, 1 Ethylidene	66

Table(3) Elemental analysis

Product	% of C	% of H	% of Se
Di-n-butyl, di- selenide	35.3	6.6	58.1
Dimethylbenzylselenide	66.0	7	27
Di-cyclohexyl selenide	59	9	32
Di-1, 1 Ethylidene, di, selenide	52.25	04.9	42.94

RESULT AND Discussion:

The dialkyl selenide and diselenide synthesis are required following condition(a)(only a single flask is required, and all reaction takes place at room temperature(b)starting material are convientally handled and in expensive on moderate scale Li(C₂H₅)₃BH¹¹(C) by product are not formed, the yield are given in(Table2). In this reaction Di-n- butyl selenide, Di-methyl benzyl selenide, Di-cyclohexyl selenide, Di 1, 1ethyledine diselenide type organoselenium are formed. Benzyl organoselenide are formed from Benzyl bromide or iodide, alkyl organoselenides are formed from alkyl bromide or iodides. Representation of symmetrical dialkylselenide, diselenide have been shown in Scheme (1a) and (1b). Se^-2and Se₂^-2can also be prepared by reduction with alkali metal-ammonia, several selenide prepared with the help of SeO₂ and carbon nucleophile. In it NaBH₄can also used as reducing agent, However Na₂Secannot prepare directly but via Se_x to NaHSe or SeO₂reacted with Grignard reagent or alkyl lithium to be formed. The exact role of tert-butyl alcohol as a cosolvent in the Li₂Se and Li₂Se₂ alkylation is uncertain¹² Li₂Se₂isprobably not significantly protonated by tert-butyl alcohol and thus prevent from depletion the alkyl halide pool by nucleophilic attack. However this should result in only a slight increase in yield. Addition of tert-butyl alcohol in this reaction to increases the polarity of reaction medium and the concentration of dissolved Li₂Se.We have also considered the possibility of tert-butyl alcohol or tert-alkoxide catalysis by addition Selenium to form a hypervalent species to enhance nucleophilicity. The (C₂H₅)₃B which is produced as by product (from commercial available Li(C₂H₅)₃BH )In this reaction, is removed as codistilled with THF and some other solvent. Unsymmetrical selenide are generally prepared by reduction of symmetrical diselenide to selenolates (RSe^-) and subsequent alkylation. However this can also be done with help of NaBH_4,Effect of Li(C₂H₅)₃BH is also similar.

CONCLUSION:

Synthesis and characterization of different series of organoselenides by various method, these organoselenides also characterized by their NMR, IR, and Elemental analysis. All organoselenide which is formed in this reaction were tested for their antimicrobial activity which show excellent antimicrobial activity against bacteria and fungi. The instant formation of such organoselenium compound will likely promote their application in pharmaceutical chemistry, microbiology and some other biochemistry.

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Received on 16.05.2017 Modified on 30.05.2017

Asian J. Research Chem. 2017; 10(3):359-361.

DOI: 10.5958/0974-4150.2017.00061.X