Ethers are a class of organic compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R -- O -- R ′, where R ′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl groups are the same on both sides of the oxygen atom it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anesthetic diethyl ether referred to as "ether". Ethers are common in organic chemistry and more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin. Ethers feature C–O–C linkage defined by a bond angle of about 110° and C–O distances of about 140 pm; the barrier to rotation about the C–O bonds is low. The bonding of oxygen in ethers and water is similar. In the language of valence bond theory, the hybridization at oxygen is sp3. Oxygen is more electronegative than carbon, thus the hydrogens alpha to ethers are more acidic than in simple hydrocarbons.
They are far less acidic than hydrogens alpha to carbonyl groups, however. Depending on the groups at R and R′, ethers are classified into two types:Simple ethers or symmetrical ethers. Mixed ethers or asymmetrical ethers. In the IUPAC nomenclature system, ethers are named using the general formula "alkoxyalkane", for example CH3–CH2–O–CH3 is methoxyethane. If the ether is part of a more-complex molecule, it is described as an alkoxy substituent, so –OCH3 would be considered a "methoxy-" group; the simpler alkyl radical is written in front, so CH3–O–CH2CH3 would be given as methoxyethane. IUPAC rules are not followed for simple ethers; the trivial names for simple ethers are a composite of the two substituents followed by "ether". For example, ethyl methyl ether, diphenylether; as for other organic compounds common ethers acquired names before rules for nomenclature were formalized. Diethyl ether is called "ether", but was once called sweet oil of vitriol. Methyl phenyl ether is anisole, because it was found in aniseed.
The aromatic ethers include furans. Acetals are another class of ethers with characteristic properties. Polyethers are compounds with more than one ether group; the crown ethers are examples of small polyethers. Some toxins produced by dinoflagellates such as brevetoxin and ciguatoxin are large and are known as cyclic or ladder polyethers. Polyether refers to polymers which contain the ether functional group in their main chain; the term glycol is reserved for low to medium range molar mass polymer when the nature of the end-group, a hydroxyl group, still matters. The term "oxide" or other terms are used for high molar mass polymer when end-groups no longer affect polymer properties; the phenyl ether polymers are a class of aromatic polyethers containing aromatic cycles in their main chain: Polyphenyl ether and Poly. Many classes of compounds with C–O–C linkages are not considered ethers: Esters, carboxylic acid anhydrides. Ether molecules cannot form hydrogen bonds with each other, resulting in low boiling points compared to those of the analogous alcohols.
The difference in the boiling points of the ethers and their isomeric alcohols becomes lower as the carbon chains become longer, as the van der Waals interactions of the extended carbon chain dominates over the presence of hydrogen bonding. Ethers are polar; the C–O–C bond angle in the functional group is about 110°, the C–O dipoles do not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structure; the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible. Cyclic ethers such as tetrahydrofuran and 1,4-dioxane are miscible in water because of the more exposed oxygen atom for hydrogen bonding as compared to linear aliphatic ethers. Other properties are: The lower ethers are volatile and flammable. Lower ethers act as anaesthetics. Ethers are good organic solvents. Simple ethers are tasteless. Ethers are quite stable chemical compounds which do not react with bases, active metals, dilute acids, oxidising agents, reducing agents.
They are of low chemical reactivity, but they are more reactive than alkanes. Epoxides and acetals are unrepresentative classes of ethers and are discussed in separate articles. Important reactions are listed below. Although ethers resist hydrolysis, their polar bonds are cloven by mineral acids such as hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers afford methyl halides: ROCH3 + HBr → CH3Br + ROHThese reactions proceed via onium intermediates, i.e. +Br−. Some ethers undergo rapid cleavage with boron tribromide to give the alkyl bromide. Depending on the substituents, some ethers can be cloven with a variety of reagents, e.g. strong base. When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether peroxide; the reaction is accelerated by light, metal catalysts, aldehydes. In addition to avoiding storage conditions to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatil
The Philosophical Magazine is one of the oldest scientific journals published in English. It was established by Alexander Tilloch in 1798; the name of the journal dates from a period when "natural philosophy" embraced all aspects of science. The first paper published in the journal carried the title "Account of Mr Cartwright's Patent Steam Engine". Other articles in the first volume include "Methods of discovering whether Wine has been adulterated with any Metals prejudicial to Health" and "Description of the Apparatus used by Lavoisier to produce Water from its component Parts and Hydrogen". Early in the nineteenth century, classic papers by Humphry Davy, Michael Faraday and James Prescott Joule appeared in the journal and in the 1860s James Clerk Maxwell contributed several long articles, culminating in a paper containing the deduction that light is an electromagnetic wave or, as he put it himself, "We can scarcely avoid the inference that light consists in transverse undulations of the same medium, the cause of electric and magnetic phenomena".
The famous experimental paper of Albert A. Michelson and Edward Morley was published in 1887 and this was followed ten years by J. J. Thomson with article "Cathode Rays" – the discovery of the electron. In 1814, the Philosophical Magazine merged with the Journal of Natural Philosophy and the Arts, otherwise known as Nicholson's Journal, to form The Philosophical Magazine and Journal. Further mergers with the Annals of Philosophy and The Edinburgh Journal of Science led to the retitling of the journal in 1840, as The London and Dublin Philosophical Magazine and Journal of Science. In 1949, the title reverted to The Philosophical Magazine. In the early part of the 20th century, Ernest Rutherford was a frequent contributor, he once told a friend to "watch out for the next issue of Philosophical Magazine. Aside from his work on understanding radioactivity, Rutherford proposed the experiments of Hans Geiger and Ernest Marsden that verified his nuclear model of the atom and led to Niels Bohr's famous paper on planetary electrons, published in the journal in 1913.
Another classic contribution from Rutherford was entitled "Collision of α Particles with Light Atoms. IV. An Anomalous Effect in Nitrogen" – an article describing no less than the first artificial transmutation of an element. In 1978 the journal was divided into two independent parts, Philosophical Magazine A and Philosophical Magazine B. Part A published papers on structure and mechanical properties while Part B focussed on statistical mechanics, electronic and magnetic properties. Since the middle of the 20th century, the journal has focused on condensed matter physics and published significant papers on dislocations, mechanical properties of solids, amorphous semiconductors and glasses; as subject area evolved and it became more difficult to classify research into distinct areas, it was no longer considered necessary to publish the journal in two parts, so in 2003 parts A and B were re-merged. In its current form, 36 issues of the Philosophical Magazine are published each year, supplemented by 12 issues of Philosophical Magazine Letters.
Previous editors of the Philosophical Magazine have been John Tyndall, J. J. Thomson, Sir Nevill Mott, William Lawrence Bragg; the journal is edited by Edward A. Davis. In 1987, the sister journal Philosophical Magazine Letters was established with the aim of publishing short communications on all aspects of condensed matter physics, it is edited by Edward A. Peter Riseborough; this monthly journal had a 2014 impact factor of 1.087. Over its 200-year history, Philosophical Magazine has restarted its volume numbers at 1, designating a new'series" each time; the journal's series are as follows: Philosophical Magazine, Series 1, volumes 1 through 68 Philosophical Magazine, Series 2, volumes 1 through 11 Philosophical Magazine, Series 3, volumes 1 through 37 Philosophical Magazine, Series 4, volumes 1 through 50 Philosophical Magazine, Series 5, volumes 1 through 50 Philosophical Magazine, Series 6, volumes 1 through 50 Philosophical Magazine, Series 7, volumes 1 through 46 Philosophical Magazine, Series 8, volumes 1 through 95 If the renumbering had not occurred, the 2015 volume would have been volume 407.
Philosophical Magazine Philosophical Magazine Letters Digitised volumes at Biodiversity Heritage Library Digitised volumes of "The London and Dublin philosophical magazine" at the Jena University Library Philosophical Magazine on Internet Archive. Philosophical Magazine Letters print: ISSN 0950-0839 Philosophical Magazine Letters online: ISSN 1362-3036
Potassium hydroxide is an inorganic compound with the formula KOH, is called caustic potash. Along with sodium hydroxide, this colorless solid is a prototypical strong base, it has many industrial and niche applications, most of which exploit its caustic nature and its reactivity toward acids. An estimated 700,000 to 800,000 tonnes were produced in 2005. About 100 times more NaOH than KOH is produced annually. KOH is noteworthy as the precursor to most soft and liquid soaps, as well as numerous potassium-containing chemicals, it is a white solid, dangerously corrosive. Most commercial samples are ca. the remainder being water and carbonates. Potassium hydroxide is sold as translucent pellets, which become tacky in air because KOH is hygroscopic. KOH contains varying amounts of water, its dissolution in water is exothermic. Concentrated aqueous solutions are sometimes called potassium lyes. At high temperatures, solid KOH does not dehydrate readily. At higher temperatures, solid KOH crystallizes in the NaCl crystal structure.
The OH group is either or randomly disordered so that the OH− group is a spherical anion of radius 1.53 Å. At room temperature, the OH− groups are ordered and the environment about the K+ centers is distorted, with K+—OH− distances ranging from 2.69 to 3.15 Å, depending on the orientation of the OH group. KOH forms a series of crystalline hydrates, namely the monohydrate KOH, the dihydrate KOH · 2H2O and the tetrahydrate KOH · 4H2O. Like NaOH, KOH exhibits high thermal stability; the gaseous species is dimeric. Because of its high stability and low melting point, it is melt-cast as pellets or rods, forms that have low surface area and convenient handling properties. About 121 g of KOH dissolve in 100 mL water at room temperature, which contrasts with 100 g/100 mL for NaOH, thus on a molar basis, KOH is less soluble than NaOH. Lower molecular-weight alcohols such as methanol and propanols are excellent solvents, they participate in an acid-base equilibrium. In the case of methanol the potassium methoxide forms: KOH + СН3ОН ↽ − ⇀ СН3ОК + H2OBecause of its high affinity for water, KOH serves as a desiccant in the laboratory.
It is used to dry basic solvents amines and pyridines. KOH, like NaOH, serves as a source of OH−, a nucleophilic anion that attacks polar bonds in both inorganic and organic materials. Aqueous KOH saponifies esters: KOH + RCOOR' → RCOOK + R'OHWhen R is a long chain, the product is called a potassium soap; this reaction is manifested by the "greasy" feel that KOH gives when touched — fats on the skin are converted to soap and glycerol. Molten KOH is used to displace other leaving groups; the reaction is useful for aromatic reagents to give the corresponding phenols. Complementary to its reactivity toward acids, KOH attacks oxides. Thus, SiO2 is attacked by KOH to give soluble potassium silicates. KOH reacts with carbon dioxide to give bicarbonate: KOH + CO2 → KHCO3 Historically, KOH was made by adding potassium carbonate to a strong solution of calcium hydroxide The salt metathesis reaction results in precipitation of solid calcium carbonate, leaving potassium hydroxide in solution: Ca2 + K2CO3 → CaCO3 + 2 KOHFiltering off the precipitated calcium carbonate and boiling down the solution gives potassium hydroxide.
This method of producing potassium hydroxide remained dominant until the late 19th century, when it was replaced by the current method of electrolysis of potassium chloride solutions. The method is analogous to the manufacture of sodium hydroxide: 2 KCl + 2 H2O → 2 KOH + Cl2 + H2Hydrogen gas forms as a byproduct on the cathode. Separation of the anodic and cathodic spaces in the electrolysis cell is essential for this process. KOH and NaOH can be used interchangeably for a number of applications, although in industry, NaOH is preferred because of its lower cost. Many potassium salts are prepared by neutralization reactions involving KOH; the potassium salts of carbonate, permanganate and various silicates are prepared by treating either the oxides or the acids with KOH. The high solubility of potassium phosphate is desirable in fertilizers; the saponification of fats with KOH is used to prepare the corresponding "potassium soaps", which are softer than the more common sodium hydroxide-derived soaps.
Because of their softness and greater solubility, potassium soaps require less water to liquefy, can thus contain more cleaning agent than liquefied sodium soaps. Aqueous potassium hydroxide is employed as the electrolyte in alkaline batteries based on nickel-cadmium, nickel-hydrogen, manganese dioxide-zinc. Potassium hydroxide is preferred over sodium hydroxide; the nickel–metal hydride batteries in the Toyota Prius use a mixture of potassium hydroxide and sodium hydroxide. Nickel–iron batteries use potassium hydroxide electrolyte. In food products, potassium hydroxide acts as a food thickener, pH control agent and food stabilizer; the FDA considers it as safe when combined with "good" manufacturing practice conditions of use. It is known in the E number system as E525. Like sodium hydroxide, potassium hydroxide attracts numerous specialized applications all of which rely on its properties as a strong chemical base with its consequent abili
Prentice Hall is a major educational publisher owned by Pearson plc. Prentice Hall publishes print and digital content for the higher-education market. Prentice Hall distributes its technical titles through the Safari Books Online e-reference service. On October 13, 1913, law professor Charles Gerstenberg and his student Richard Ettinger founded Prentice Hall. Gerstenberg and Ettinger took their mothers' maiden names—Prentice and Hall—to name their new company. Prentice Hall was acquired by Gulf+Western in 1984, became part of that company's publishing division Simon & Schuster. Publication of trade books ended in 1991. Simon & Schuster's educational division, including Prentice Hall, was sold to Pearson by G+W successor Viacom in 1998. There were two or more authors, their books turned up missing. One book'The Roof Builder's Handbook' is still being sold in 2018 for as much as $230 per new copy, but the author William C. McElroy was told by Pearson that all new books were either destroyed or went missing in 1995.
Some 2,385 copies are missing. Prentice Hall is the publisher of Magruder's American Government as well as Biology by Ken Miller and Joe Levine, their artificial intelligence series includes Artificial Intelligence: A Modern Approach by Stuart J. Russell and Peter Norvig and ANSI Common Lisp by Paul Graham, they published the well-known computer programming book The C Programming Language by Brian Kernighan and Dennis Ritchie and Operating Systems: Design and Implementation by Andrew S. Tanenbaum. Other titles include Dennis Nolan's Big Pig, Monster Bubbles: A Counting Book, Wizard McBean and his Flying Machine, Witch Bazooza, Llama Beans, The Joy of Chickens. A Prentice Hall subsidiary, Reston Publishing, was in the foreground of technical-book publishing when microcomputers were first becoming available, it was still unclear who would be buying and using "personal computers," and the scarcity of useful software and instruction created a publishing market niche whose target audience yet had to be defined.
In the spirit of the pioneers who made PCs possible, Reston Publishing's editors addressed non-technical users with the reassuring, mildly experimental, Computer Anatomy for Beginners by Marlin Ouverson of People's Computer Company. They followed with a collection of books, by and for programmers, building a stalwart list of titles relied on by many in the first generation of microcomputers users. Prentice Hall International Series in Computer Science Prentice Hall website Prentice Hall School website Prentice Hall Higher Education website Prentice Hall Professional Technical Reference website
Royal Society of Chemistry
The Royal Society of Chemistry is a learned society in the United Kingdom with the goal of "advancing the chemical sciences". It was formed in 1980 from the amalgamation of the Chemical Society, the Royal Institute of Chemistry, the Faraday Society, the Society for Analytical Chemistry with a new Royal Charter and the dual role of learned society and professional body. At its inception, the Society had a combined membership of 34,000 in the UK and a further 8,000 abroad; the headquarters of the Society are at Burlington House, London. It has offices in Thomas Graham House in Cambridge where RSC Publishing is based; the Society has offices in the United States at the University City Science Center, Philadelphia, in both Beijing and Shanghai and Bangalore, India. The organisation carries out research, publishes journals and databases, as well as hosting conferences and workshops, it is the professional body for chemistry in the UK, with the ability to award the status of Chartered Chemist and, through the Science Council the awards of Chartered Scientist, Registered Scientist and Registered Science Technician to suitably qualified candidates.
The designation FRSC is given to a group of elected Fellows of the society who have made major contributions to chemistry and other interface disciplines such as biological chemistry. The names of Fellows are published each year in The Times. Honorary Fellowship of the Society is awarded for distinguished service in the field of chemistry; the president is elected biennially and wears a badge in the form of a spoked wheel, with the standing figure of Joseph Priestley depicted in enamel in red and blue, on a hexagonal medallion in the centre. The rim of the wheel is gold, the twelve spokes are of non-tarnishable metals; the current president is Dame Carol V. Robinson. Past presidents of the society have been: The following are membership grades with post-nominals: Affiliate: The grade for students and those involved in chemistry who do not meet the requirements for the following grades. AMRSC: Associate Member, Royal Society of Chemistry The entry level for RSC membership, AMRSC is awarded to graduates in the chemical sciences.
MRSC: Member, Royal Society of Chemistry Awarded to graduates with at least 3 years' experience, who have acquired key skills through professional activity FRSC: Fellow of the Royal Society of Chemistry Fellowship may be awarded to nominees who have made an outstanding contribution to chemistry. HonFRSC: Honorary Fellow of the Society Honorary Fellowship is awarded for distinguished service in the field of chemistry. CChem: Chartered Chemist The award of CChem is considered separately from admission to a category of RSC membership. Candidates need to be MRSC or FRSC and demonstrate development of specific professional attributes and be in a job which requires their chemical knowledge and skills. CSci: Chartered Scientist The RSC is a licensed by the Science Council for the registration of Chartered Scientists. EurChem: European Chemist The RSC is a member of the European Communities Chemistry Council, can award this designation to Chartered Chemists. MChemA: Mastership in Chemical Analysis The RSC awards this postgraduate qualification, the UK statutory qualification for practice as a Public Analyst.
It requires candidates to submit a portfolio of suitable experience and to take theory papers and a one-day laboratory practical examination. The qualification GRSC was awarded from 1981 to 1995 for completion of college courses equivalent to an honours chemistry degree and overseen by the RSC, it replaced the GRIC offered by the Royal Institute of Chemistry. The society is organised around 9 divisions, based on subject areas, local sections, both in the United Kingdom and overseas. Divisions cover broad areas of chemistry but contain many special interest groups for more specific areas. Analytical Division for analytical chemistry and promoting the original aims of the Society for Analytical Chemistry. 12 Subject Groups. Dalton Division, named after John Dalton, for inorganic chemistry. 6 Subject Groups. Education Division for chemical education. 4 Subject Groups. Faraday Division, named after Michael Faraday, for physical chemistry and promoting the original aims of the Faraday Society. 14 Subject Groups.
Organic Division for organic chemistry. 6 Subject Groups. Chemical Biology Interface Division. 2 Subject Groups. Environment and Energy Division. 3 Subject Groups. Materials Chemistry Division. 4 Subject Groups. Industry and Technology Division. 13 Subject Groups. There are 12 subjects groups not attached to a division. There are 35 local sections covering the United Ireland. In countries of the Commonwealth of Nations and many other countries there are Local Representatives of the society and some activities; the society is a not-for-profit publisher: surplus made by its publishing business is invested to support its aim of advancing the chemical sciences. In addition to scientific journals, including its flagship journals Chemical Communications, Chemical Science and Chemical Society Reviews, the society publishes: Education in Chemistry for teachers. A free online journal for chemistry educators, Chemistry Education Research and Practice. A general chemistry magazine Chemistry World, sent monthly to all members of the Society throughout the world.
The editorial board consists of 10 industrial chemists. It was first published in January 2004, it replaced C
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments; these parts, or groups, must be protected. For example, lithium aluminium hydride is a reactive but useful reagent capable of reducing esters to alcohols, it will always react with carbonyl groups, this cannot be discouraged by any means. When a reduction of an ester is required in the presence of a carbonyl, the attack of the hydride on the carbonyl has to be prevented. For example, the carbonyl is converted into an acetal; the acetal is called a protecting group for the carbonyl. After the step involving the hydride is complete, the acetal is removed, giving back the original carbonyl; this step is called deprotection.
Protecting groups are more used in small-scale laboratory work and initial development than in industrial production processes because their use adds additional steps and material costs to the process. However, the availability of a cheap chiral building block can overcome these additional costs. Protection of alcohols: Acetyl -- Removed by base. Benzoyl – Removed by acid or base, more stable than Ac group. Benzyl – Removed by hydrogenolysis. Bn group is used in sugar and nucleoside chemistry. Β-Methoxyethoxymethyl ether – Removed by acid. Dimethoxytrityl, – Removed by weak acid. DMT group is used for protection of 5'-hydroxy group in nucleosides in oligonucleotide synthesis. Methoxymethyl ether – Removed by acid. Methoxytrityl – Removed by acid and hydrogenolysis. P-Methoxybenzyl ether – Removed by acid, hydrogenolysis, or oxidation. Methylthiomethyl ether – Removed by acid. Pivaloyl – Removed by acid, base or reductant agents, it is more stable than other acyl protecting groups. Tetrahydropyranyl – Removed by acid.
Tetrahydrofuran – Removed by acid. Trityl – Removed by acid and hydrogenolysis. Silyl ether – Removed by acid or fluoride ion.. TBDMS and TOM groups are used for protection of 2'-hydroxy function in nucleosides in oligonucleotide synthesis. Methyl ethers – Cleavage is by TMSI in dichloromethane or acetonitrile or chloroform. An alternative method to cleave methyl ethers is BBr3 in DCM Ethoxyethyl ethers – Cleavage more trivial than simple ethers e.g. 1N hydrochloric acid Protection of amines: Carbobenzyloxy group – Removed by hydrogenolysis p-Methoxybenzyl carbonyl group – Removed by hydrogenolysis, more labile than Cbz tert-Butyloxycarbonyl group – Removed by concentrated strong acid, or by heating to >80 °C. 9-Fluorenylmethyloxycarbonyl group – Removed by base, such as piperidine Acetyl group is common in oligonucleotide synthesis for protection of N4 in cytosine and N6 in adenine nucleic bases and is removed by treatment with a base, most with aqueous or gaseous ammonia or methylamine. Ac is too stable to be removed from aliphatic amides.
Benzoyl group is common in oligonucleotide synthesis for protection of N4 in cytosine and N6 in adenine nucleic bases and is removed by treatment with a base, most with aqueous or gaseous ammonia or methylamine. Bz is too stable to be removed from aliphatic amides. Benzyl group -- Removed by hydrogenolysis Carbamate group -- Removed by mild heating. P-Methoxybenzyl – Removed by hydrogenolysis, more labile than benzyl 3,4-Dimethoxybenzyl – Removed by hydrogenolysis, more labile than p-methoxybenzyl p-methoxyphenyl group – Removed by ammonium cerium nitrate Tosyl group – Removed by concentrated acid & strong reducing agents Troc group – Removed by Zn insertion in the presence of acetic acid Other Sulfonamides groups – Removed by samarium iodide, tributyltin hydride Protection of carbonyl groups: Acetals and Ketals – Removed by acid; the cleavage of acyclic acetals is easier than of cyclic acetals. Acylals – Removed by Lewis acids. Dithianes – Removed by metal salts or oxidizing agents. Protection of carboxylic acids: Methyl esters -- Removed by base.
Benzyl esters – Removed by hydrogenolysis. Tert-Butyl esters – Removed by acid and some reductants. Esters of 2,6-disubstituted phenols – Removed at room temperature by DBU-catalyzed methanolysis under high-pressure conditions. Silyl esters – Removed by acid and organometallic reagents. Orthoesters – Removed by mild aqueous acid to form ester, removed according to ester properties. Oxazoline – Removed by strong hot acid or alkali, but not e.g. LiAlH4, organolithium reagents or Grignard reagents 2-cyanoethyl – removed by mild base; the group is used in oligonucleotide synthesis. Methyl – removed by strong nucleophiles e.c. thiophenole/TEA. Propargyl alcohols in the Favorskii reactio
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as RO −. Alkoxides are strong bases and, when R is not good nucleophiles and good ligands. Alkoxides, although not stable in protic solvents such as water, occur as intermediates in various reactions, including the Williamson ether synthesis. Transition metal alkoxides are used for coatings and as catalysts. Enolates are unsaturated alkoxides derived by deprotonation of a C-H bond adjacent to a ketone or aldehyde; the nucleophilic center for simple alkoxides is located on the oxygen, whereas the nucleophilic site on enolates is delocalized onto both carbon and oxygen sites. Phenoxides are close relatives of the alkoxides, in which the alkyl group is replaced by a derivative of benzene. Phenol is more acidic than a typical alcohol, they are, however easier to handle, yield derivatives that are more crystalline than those of the alkoxides. Alkali metal alkoxides are oligomeric or polymeric compounds when the R group is small.
The alkoxide anion is a good bridging ligand, thus many alkoxides feature M2O or M3O linkages. In solution, the alkali metal derivatives exhibit strong ion-pairing, as expected for the alkali metal derivative of a basic anion. Alkoxides can be produced by several routes starting from an alcohol. Reducing metals react directly with alcohols to give the corresponding metal alkoxide; the alcohol serves as an acid, hydrogen is produced as a by-product. A classic case is sodium methoxide produced by the addition of sodium metal to methanol: 2 CH3OH + 2 Na → 2 CH3ONa + H2Other alkali metals can be used in place of sodium, most alcohols can be used in place of methanol. Another similar reaction occurs when an alcohol is reacted with a metal hydride such as NaH; the metal hydride removes the hydrogen atom from the hydroxyl group and forms a negatively charged alkoxide ion. Titanium tetrachloride reacts with alcohols to give the corresponding tetraalkoxides, concomitant with the evolution of hydrogen chloride: TiCl4 + 4 2CHOH → Ti4 + 4 HClThe reaction can be accelerated by the addition of a base, such as a tertiary amine.
Many other metal and main group halides can be used instead of titanium, for example SiCl4, ZrCl4, PCl3. Many alkoxides are prepared by salt-forming reactions from a metal chloride and sodium alkoxide: n NaOR + MCln → Mn + n NaClSuch reactions are favored by the lattice energy of the NaCl, purification of the product alkoxide is simplified by the fact that NaCl is insoluble in common organic solvents. Many alkoxides can be prepared by anodic dissolution of the corresponding metals in water-free alcohols in the presence of electroconductive additive; the metals may be etc.. The conductive additive may be quaternary ammonium halide, or other; some examples of metal alkoxides obtained by this technique: Ti4, Nb210, Ta210, 2, Re2O36, Re4O612, Re4O610. The alkoxide ion can react with a primary alkyl halide in an SN2 reaction to form a methyl ether. Metal alkoxides hydrolyse with water according to the following equation: 2 LnMOR + H2O → 2O + 2 ROHwhere R is an organic substituent and L is an unspecified ligand A well-studied case is the irreversible hydrolysis of titanium ethoxide: 1/n n + 2 H2O → TiO2 + 4 HOCH2CH3By controlling the stoichiometry and steric properties of the alkoxide, such reactions can be arrested leading to metal-oxy-alkoxides, which are oligonuclear complexes.
Other alcohols can be employed in place of water. In this way one alkoxide can be converted to another, the process is properly referred to as alcoholysis; the position of the equilibrium can be controlled by the acidity of the alcohol. More the alcoholysis can be controlled by selectively evaporating the more volatile component. In this way, ethoxides can be converted to butoxides. In the transesterification process, metal alkoxides react with esters to bring about an exchange of alkyl groups between metal alkoxide and ester. With the metal alkoxide complex in focus, the result is the same as for alcoholysis, namely the replacement of alkoxide ligands, but at the same time the alkyl groups of the ester are changed, which can be the primary goal of the reaction. Sodium methoxide, for example, is used for this purpose, a reaction, relevant to the production of "bio-diesel". Many metal alkoxide compounds feature oxo-ligands. Oxo-ligands arise via the hydrolysis accidentally, via ether elimination: 2 LnMOR → 2O + R2OAdditionally, low valent metal alkoxides are susceptible to oxidation by air Characteristically, transition metal alkoxides are polynuclear, they contain more than one metal.
Alkoxides are sterically undemanding and basic ligands that tend to bridge metals. Upon the isomorphic substitution of metal atoms close in properties crystalline complexes of variable composition are formed; the metal ratio in such compounds can vary over a broad range. For instance, the substitution of molybdenum and tungsten for rhenium in the complexes Re4O6−y12+y allo