CHM 621 Newer Reagents in Organic Synthesis

I thank the Indian Institute of Technology, Guwahati for the initial financial support and for all the facilities made available to me. I thank my father for the lessons he taught me when I was a child and...for his blessings that are always with me.

Synthesis and structural assessment of diperoxovanadate(V) complexes containing 3,5-dimethylpyrazole as the heteroligand

Introduction and scope of the work

In another manifestation of transition metal reaction chemistry, the oxidation chemistry of oxochrome(VI), with special reference to fluorochromate(VI), is presented for brief discussion. This section, while presenting a non-exhaustive description of the available chromium(VI) reagents, highlights the fact that the search for better performing oxidizing reagents still continues.

Methods of preparation of starting materials, elemental analyses and the details of instrumental techniques used for

From this, a common bond emerged between the two parts of the entire text of the diploma thesis, which deals with the treasure of oxidation chemistry with the help of transition metals. A critical presentation of the current importance of selected problems in the chemical sciences scenario leads to a broad and rewarding scope of work that is included in the thesis and much more.

Peroxo-metal mediated environmentally favorable route to brominating agents and protocols for bromination of organics

Part A: Quaternary ammonium tribromides (QATBs) [QA = tetramethyl-ammonium (TMA), tetraethylammonium (TEA),

This chapter also discusses the successful synthesis of tetramethylammonium tribromide, TMATB, (CH3)4NBr3, tetraethylammonium tribromide, TEATB, (C2H5)4NBr3, and cetyltrimethylammonium tribromide, CTMATB, (C16H33)(CH3)3NBr3. The chemical synthesis of any compound is always followed by its characterization using physicochemical methods.

Synthesis and structural assessment of diperoxovanadate(V) complexes containing 3,5-dimethylpyrazole as the heteroligand

The study of electronic structures of the metal-dioxygen unit is of interest in connection with binding of O2 to the metal centers in metalloenzymes, oxygen-carrying proteins, and also with catalytic oxidations. Some essential points of similarity, between [VO2F(dmpz)2] and [VO(O2)2(dmpz)]– in terms of the oxidation state of the metal and similarities in.

Oxidation of selected organic substrates using a new reagent,

Electronic spectrum TMATB Electronic spectrum TEATB Electronic spectrum TBATB Electronic spectrum CTMATB Far-IR spectrum TMATB Far-IR spectrum TEATB Far-IR spectrum TBATB Far-IR spectrum CTMATB. 1H NMR spectrum of 2,3-dibromo-3(4-methoxy-phenyl)-1-phenyl-propan-1-one IR spectrum of 2,3-dibromo-3-phenyl-propionic acid methyl ester.

INTRODUCTION AND SCOPE OF WORK

One of the main reasons for the commercial importance of peroxo-metallates lies in the fact that the peroxide (O22-) is activated by a higher-valent transition. Although some results have been published, manuscripts based on the rest are in preparation or in preparation.

ANALYSES AND THE DETAILS OF

INSTRUMENTAL TECHNIQUES USED FOR CHARACTERIZATION AND STRUCTURAL

ASSESSMENT OF THE COMPOUNDS

Detailed procedures used for the preparation of different starting materials are described in this chapter. Also described herein are the details of the methods used for quantitative determination of various ingredients and the relevant details of the instruments/equipment used for the characterization and structural assessment of the newly synthesized compounds. All the chemicals and solvents used for the present work were of analytical grade quality.

Following are the sources of chemicals and solvents: s.d.fine-chem ltd, Qualigens Fine Chemicals, E.Merck (India) Limited, Sisco Research Laboratories Pvt.

Preparation of starting materials

The stirrer was removed and the reaction mixture was left in an ice chest or refrigerator overnight. By vigorously scratching the walls of the vessel with a glass rod, crystals began to emerge. H 2 O 2 was added to aid dissolution of the vanadium oxide by oxidizing the small portion of vanadium(IV) generally present in the commercial product.

The exact color of the solution depended on the pH (A deep yellow color would indicate that too little K2CO3 was used while a colorless solution would indicate that too much K2CO3 was used).

Elemental analyses

An accurately weighed amount (about 0.1 g) of a fluoride-containing compound of chromium was dissolved in 150 ml of water. The volume of AgNO3 in the filtrate thus found was subtracted from the amount originally added. To this was added an accurately weighed amount (about 0.1 g) of peroxo compound followed by the addition of 7 mL of 5M H2SO4.

To a freshly prepared 2 M sulfuric acid solution, containing an appropriate amount of potassium iodide (~2 g in 100 ml), an accurately weighed amount (about 0.1 g) of a peroxo compound was added with stirring.

Particulars of Instruments/Equipment Used for the Following Physico-chemical Studies

The maximum intensity corrections based on the standard reflections were less than 1% for each. The linear absorption coefficients, scattering factors for the atoms and the anomalous dispersion corrections are taken from the International Tables for X-ray Crystallography. The refinement was performed using full-matrix least squares techniques using anisotropic thermal parameters for all non-hydrogen atoms.

Some H-atoms could be located in the differential maps in each case, the rest were calculated assuming the ideal geometry of the atom in question.

PEROXO-METAL MEDIATED

ENVIRONMENTALLY FAVOURABLE ROUTE TO BROMINATING AGENTS AND

PROTOCOLS FOR BROMINATION OF ORGANICS

Although bromoorganic substances have a relatively small share in the entire field of organic chemistry, brominated organic products, and especially bromoaromatics, enjoy a very special status due to their use in the manufacture of a range of bulk and fine chemicals, including flame retardants, disinfectants , antibacterial and antiviral drugs.1 The commercial importance of organic bromine derivatives lies in their use as precursors in the manufacture of pharmaceuticals, agricultural chemicals and other specialty chemicals. From the knowledge gained from the structure and reactivity studies of VBrPO, it is also understood that the enzyme first interacts with H2O2 to activate the coordinated peroxide ligand so that it can oxidize bromide available in the natural marine environment. What was also observed was that, as in the VBrPO reactions, the V(V) center did not undergo any reduction but retained its identity as far as the oxidation state is concerned.

Knowledge obtained from such studies together with the existence of Br3– in solution (λ=267 nm)16-18 in high concentration led us to believe that Br3– can be generated not only in solution but also in the solid state can be isolated by providing an appropriate counter cation.

Part A

RAY STRUCTURE DETERMINATION OF TBATB 34

Bromination of cyclohexene: To a mixed solution of 0.57 mL (10 mmol) of cyclohexene dissolved in 5 mL of acetonitrile was added 3.45 g (11 mmol) of TMATB dissolved in 15 mL of the same solvent. The specific molar ratios of the substrates and the reagent and the corresponding percentage yields of the products are listed in Table 3.2. Bromination of anthracene: To a mixed solution of 0.5 g (2.8 mmol) of anthracene dissolved in 5 mL of acetonitrile (2 mL of CH2Cl2 was added as cosolvent) was added 1.55 g (4.2 mmol) of TEATB dissolved in 15 mL same solvent.

Bromination of chalcone: To a stirred solution of 0.21 g (1 mmol) chalcone dissolved in 5 ml of acetonitrile was added 0.524 g (1 mmol) of CTMATB dissolved in 15 ml of the same solvent.

RESULTS AND DISCUSSION

Thus, the synthesis of tribromides described here not only provides easy access to such compounds, but also evidences the formation of Br3- in solution. The solution electrical conductivities (ΛM) of the four tribromides recorded at room temperature in 10-3 M acetonitrile solutions lie in the range 115-165 Ω-. In addition to their biomimetic synthesis (cf. VBrPO activity), followed by the establishment of their identity, an analysis of the chemical composition, particularly focused on the presence of tribromide (Br3–) (Figure 3.13) suggests that these compounds can be considered as storage of Br2.

After success in synthesizing the reagents using the new methodology, the mission would be complete if their oxidative bromination profiles were found to be satisfactory.

Part B

These are (i) activation of dioxygen by the interaction of H2O2 with vanadium(V), which leads to the formation of peroxovanadium(V) species (λ = 430 nm)37 in solution, followed by (ii) oxidation of bromide with peroxovanadium(V) ) an intermediate which finally leading to the formation of Br3– (λ = 266 nm) 16, 17 as the active brominating agent, and finally (iii) bromination of organic substrates to give organobromocompounds. The pH values ​​recorded at the beginning and after completion of the reaction were approx. Quite interestingly, regioselective bromination of an activated aromatic compound such as acetanilide led exclusively to the corresponding p-bromo derivative, a similar observation being made for aniline, o-cresol/and m-cresol (Table 3.8), while when under similar experimental conditions of phenol they produced 2,4,6-tribromophenol.

Further effectiveness of the methodology lies in the bromination of alkyne systems, as demonstrated by the facile bromination of 2-butyne-1,4-diol.

CONCLUDING REMARKS

A very significant and timely point is the importance of the chemistries involved in the synthesis of tribromides and their reactions with organic substrates (see Part A of this Chapter) in the context of "Green Chemistry". Interestingly, the fundamental chemistry involved in the synthesis of quaternary ammonium tribromides (QATB) provided hints regarding the involvement of a peroxo-vanadium(V) intermediate leading to the generation of Br3-. Therefore, this leaves a possibility for direct oxidative organic brominations without isolating the tribromides in the solid state.

The science involved in the research described in Chapter 3 therefore deserves much attention from modern chemists.

Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th Edition, Part A, Wiley, New York, 1997, p.169.

SYNTHESIS AND STRUCTURAL ASSESSMENT OF DIPEROXOVANADATE(V) COMPLEXES

THE HETEROLIGAND

The study of the literature reveals that diperoxovanadium (V) compounds are actively involved in a very important biochemical process, i.e., insulin-mimicking activity. evidence strongly suggesting that peroxovanadates are responsible for the observed effects.2 In fact, the synergistic insulin-like effects of hydrogen peroxide with vanadates exceed those seen with vanadates or hydrogen peroxide alone.3. The sources of chemicals and solvents have already been given in Chapter 2. Quantification of the elements was carried out by the methods described in Chapter 2. Details of all the equipment used for the physicochemical studies are also given in Chapter 2. The total amount of compound isolated in seven or eight days from the date of isolation of the first batch of crystals.

Total amount of the compound was isolated within a week from the date of isolation of the first harvest of crystals.

RESULTS AND DISCUSSIONS

The 1 H NMR spectrum of dmpzH[VO(O 2 ) 2 (dmpz)] against TMS evidences for the occurrence of both coordinated dimethylpyrazole ligand and 3,5-

Ideally, the structural delineation by X-ray crystallographic studies would be preferred to confirm the structure of the complex, [VO(O2)2(dmpz)] ion. However, a strong similarity between the vibrational spectral bands of [VO(O2)2(dmpz)]– and [VO2F(dmpz)2], regarding the vanadium  dmpz  bond, the presence of vanadium( V) in both cases, and the availability of ​​the X-ray crystallographically generated structural data regarding the presence of V  N (dmpz) of the dmpz ligand bound to the metal center in a. One of the important concerns has been to generate suitable peroxovanadate(V) complexes with improved insulinomimetic properties.

Also significant is the less usual six-coordination geometry of the metal center in a heteroligand peroxo environment.

OXIDATION OF SELECTED ORGANIC SUBSTRATES USING A NEW REAGENT, 3,5-

DIMETHYLPYRAZOLIUM

Metal-Acetylacetonates: Newer Strategies for Direct Synthesis and Reactions, Evidence for Ion-Association/Ion Pair Formation in