Oxophilicity is the tendency of certain chemical compounds to form

oxide An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...

s by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

or abstraction of an oxygen atom from another molecule, often from organic compounds. The term is often used to describe metal centers, commonly the early

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

s such as

titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

niobium Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...

, and

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isolat ...

. Oxophilicity is often stated to be related to the hardness of the element, within the

HSAB theory HSAB concept is a jargon for "hard and soft Lewis acids and bases, (Lewis) acids and bases". HSAB is widely used in chemistry for explaining stability of chemical compound, compounds, reaction mechanisms and pathways. It assigns the terms 'hard' o ...

( hard and soft (Lewis) acids and bases), but it has been shown that oxophilicity depends more on the electronegativity and effective nuclear charge of the element than on its hardness. This explains why the early transition metals, whose electronegativities and effective nuclear charges are low, are very oxophilic. Many

main group In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arra ...

compounds are also oxophilic, such as derivatives of

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

, and

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...

(III). The handling of oxophilic compounds often requires

air-free technique Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less comm ...

Examples

Complexes of oxophilic metals typically are prone to

. For example, the high valent chlorides hydrolyze rapidly to give oxides: :TiCl₄ + 2 H₂O → TiO₂ + 4 HCl These reactions proceed via oxychloride intermediates. For example, WOCl₄ results from the partial hydrolysis of

tungsten hexachloride Tungsten hexachloride is the chemical compound of tungsten and chlorine with the formula WCl6. This dark violet blue species exists as a volatile solid under standard conditions. It is an important starting reagent in the preparation of tungsten ...

. Hydroxide-containing intermediates are rarely observed for oxophilic metals. In contrast, the

anhydrous A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achie ...

halides of the later metals tend to

hydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

, not hydrolyze, and they often form

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

s. Reduced complexes of oxophilic metals tend to generate oxides by reaction with oxygen. Typically the oxide-ligand is bridging, e.g. :2 (C₅H₅)₂TiCl + 1/2 O₂ → ₂O Only in rare cases do the products of oxygenation feature terminal oxo ligands.

Applications of oxophilicity in synthesis

Oxophilic reagents are often used to extract or exchange oxygen centers in organic substrates, especially carbonyls (esters, ketones, amides) and epoxides. The highly oxophilic reagent generated from

and

butyl lithium Butyllithium may refer to one of 5 isomeric organolithium reagents of which 3 are commonly used in chemical synthesis: * ''n''-Butyllithium, abbreviated BuLi or nBuLi * ''sec''-Butyllithium, abbreviated ''sec''-BuLi or sBuLi, has 2 stereoisomers, ...

is useful for the deoxygenation of

epoxide In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for ...

s. Such conversions are sometimes valuable in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. In the

McMurry reaction The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to form an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent. The reaction is named after its co-discoverer, ...

, ketones are converted into alkenes using oxophilic reagents: :2 R₂CO + Ti → R₂C=CR₂ + TiO₂ Similarly,

Tebbe's reagent Tebbe's reagent is the organometallic compound with the formula (C5H5)2TiCH2ClAl(CH3)2. It is used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the R2C=O group into the related R2C=CH2 derivative. It ...

is used in olefination reactions: : Cp₂TiCH₂AlCl(CH₃)₂ + R₂C=O → Cp₂TiO + 0.5 (AlCl(CH₃)₂)₂ + R₂C=CH₂ Oxophilic main group compounds are also well known and useful. The highly oxophilic reagent Si₂Cl₆ stereospecifically deoxygenates

phosphine oxide Phosphine oxides are phosphorus compounds with the formula OPX3. When X = alkyl or aryl, these are organophosphine oxides. Triphenylphosphine oxide is an example. An inorganic phosphine oxide is phosphoryl chloride (POCl3). Structure and bonding ...

Phosphorus pentasulfide Phosphorus pentasulfide is the inorganic compound with the formula (monomer) or (dimer). This yellow solid is the one of two phosphorus sulfides of commercial value. Samples often appear greenish-gray due to impurities. It is soluble in carbon d ...

and the related

Lawesson's reagent Lawesson's reagent (LR) is a chemical compound used in organic synthesis as a thiation agent. Lawesson's reagent was first made popular by Sven-Olov Lawesson, who did not, however, invent it. Lawesson's reagent was first made in 1956 during a sys ...

convert certain organic carbonyls to the corresponding sulfur derivatives: :P₄S₁₀ + ''n'' R₂C=O → P₄S_10−''n''O_n + ''n'' R₂C=S Owing to the high stability of

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

, many carbon compounds such as

phosgene Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, espe ...

are oxophilic. This reactivity is used for recycling of

triphenylphosphine oxide Triphenylphosphine oxide (often abbreviated TPPO) is the organophosphorus compound with the formula OP(C6H5)3, also written as Ph3PO or PPh3O (Ph = C6H5). This colourless crystalline compound is a common but potentially useful waste product in ...

: :OPPh₃ + COCl₂ → Cl₂PPh₃ + CO₂

References

{{Reflist Acid–base chemistry Inorganic chemistry