| n-Butyllithium | |
|---|---|
 |
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| IUPAC name | butyllithium, tetra-μ3-butyl-tetralithium |
| Other names | NBL, BuLi, 1-lithiobutane |
| Identifiers | |
| CAS number | [109-72-8] |
| SMILES | CCCC[Li] |
| Properties | |
| Molecular formula | C4H9Li |
| Molar mass | 64. IUPAC Nomenclature is a system of naming Chemical compounds and of describing the science of Chemistry in general CAS registry numbers are unique numerical identifiers for Chemical compounds Polymers biological sequences mixtures and Alloys They are also referred to A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Molar mass, symbol M, is the Mass of one mole of a substance ( Chemical element or Chemical compound) 05 g/mol |
| Appearance | colorless crystals unstable usually obtained as soln |
| Density | 0. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 68 g/cm³, solvent defined |
| Melting point |
-76 °C (<273 K) |
| Boiling point |
decomposes |
| Solubility in water | reacts violently |
| Solubility in diethyl ether | soluble |
| Acidity (pKa) | >35 (need source) |
| Structure | |
| Molecular shape | tetrameric in solution |
| Dipole moment | 0 D |
| Hazards | |
| Main hazards | inflames in air, decomposes to corrosive LiOH |
| Related compounds | |
| Related organolithium reagents |
sec-butyllithium tert-butyllithium hexyllithium methyllithium |
| Related compounds | lithium hydroxide |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references |
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n-Butyllithium (abbreviated BuLi) is the most prominent organolithium reagent. An organolithium reagent is an Organometallic compound with a direct bond between a Carbon and a Lithium atom It enjoys wide use as a polymerisation initiator in the production of elastomers such as polybutadiene or styrene-butadiene-styrene (SBS). In Polymer chemistry, polymerization is a process of reacting Monomer Molecules together in a Chemical reaction to form three-dimensional networks An elastomer is a Polymer with the property of Elasticity. The term which is derived from elastic polymer, is often used interchangeably with the term Polybutadiene is a Synthetic rubber that is a Polymer formed from the Polymerization of the Monomer 13-butadiene. Styrene-Butadiene ( SBR) is an Elastomeric Copolymer consisting of Styrene and Butadiene. Also, it is broadly employed as a strong base (superbase) in organic synthesis, both industrially and in the laboratory. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and In Chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase but most chemists would accept
Butyllithium is commercially available as solutions (15%, 25%, 2 M, 2. 5 M, 10 M, etc. ) in alkanes such as pentane, hexanes, or heptanes. Annual worldwide production and consumption of butyllithium and other organolithium compounds is estimated at 1800 metric tonnes.
Although it is a colourless solid, n-butyllithium is usually encountered as a pale yellow solution in alkanes. Such solutions are stable indefinitely if properly stored,[1] but in practice, they degrade upon aging. Fine white precipitate (lithium hydride) is deposited and the color changes to orange. Lithium hydride ( Li[[Hydride H]] is the compound of Lithium and hydrogen
Contents |
Structure and bonding
n-BuLi exists as a cluster both in the solid state and in a solution in most solvents. An organolithium reagent is an Organometallic compound with a direct bond between a Carbon and a Lithium atom The tendency to aggregate is common for organolithium compounds. The aggregates are held together by delocalized covalent bonds between lithium and the terminal carbon of the butyl chain. [2] In the case of n-BuLi, the clusters are tetrameric (in ether) or hexameric (in cyclohexane). The tetrahedral cluster is a distorted cubane structure with Li and CH2R groups at alternating vertices. An equivalent description describes the tetramer as a Li4 tetrahedron interpenetrated with a tetrahedron [CH2R]4. Bonding within the cluster is related to that used to describe diborane, but more complex since eight atoms are involved. Reflecting its "electron-deficient character," n-butyllithium is highly reactive toward Lewis bases.
Due to the large difference between the electronegativities of carbon (2.55) and lithium (0.98), the C-Li bond is highly polarized. " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons The charge separation has been estimated to be 55-95%. For practical purposes, n-BuLi can often be considered to react as the butyl anion, n-Bu−, and a lithium cation, Li+ even though this model is incorrect: n-BuLi is not ionic.
Preparation
The standard preparation for n-BuLi is reaction of bromobutane or chlorobutane with Li metal:[1]
- 2 Li + C4H9X → C4H9Li + LiX
- where X = Cl, Br
The lithium for this reaction contains 1-3% sodium. Solvents used for this preparation include benzene, cyclohexane, and diethyl ether. When BuBr is the precursor, the product is a homogeneous solution, consisting of a mixed cluster containing both LiBr and LiBu. BuLi forms a weaker complex with LiCl, so that the reaction of BuCl with Li produces a precipitate of LiCl. Lithium chloride is a Chemical compound with the formula Li[[Chlorine Cl]]
Reactions
Butyllithium is a strong base, but it is also a powerful nucleophile and reductant, depending on the other reactants. Furthermore, in addition to being a strong nucleophile, n-BuLi binds to aprotic Lewis bases, such as ethers and tertiary amines, which disagregate the clusters by binding to the lithium centers. Its use as a strong base is referred to as metalation. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Metalation (metallation is a Chemical reaction which results in a Metal atom beingattached to a (usually organic) molecule Reactions are typically conducted in tetrahydrofuran and diethyl ether, which are good solvents for the resulting organolithium derivatives (see below). "THF" redirects here For other uses see THF (disambiguation. Diethyl ether, also known as ether and ethoxyethane, is a clear colorless and highly Flammable liquid with a low Boiling point and a
Metalation
One of the most useful chemical properties of n-BuLi is its ability to deprotonate a wide range of weak Bronsted acids. An organolithium reagent is an Organometallic compound with a direct bond between a Carbon and a Lithium atom In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are t-Butyllithium and s-butyllithium are more basic still. n-BuLi can deprotonate (that is, metalate) many types of C-H bonds, especially where the conjugate base is stabilized by electron delocalization or one or more heteroatoms (non carbon atoms). Within the Brønsted - Lowry ( protonic) theory of acids and bases, a conjugate acid is the acid member HX of a pair of two compounds that transform In chemistry delocalized electrons are Electrons in a Molecule that are not associated with a single Atom or to a Covalent bond. Examples include acetylenes (H-CC-R), methyl sulfides (H-CH2SR), thioacetals (H-CH(SR)2, e. g. dithiane), methylphosphines (H-CH2PR2), furans, thiophenes and ferrocene (Fe(H-C5H4)(C5H5). Furan, also known as furane and furfuran, is a heterocyclic Organic compound. Thiophene is the Heterocyclic compound with the formula C4H4S Ferrocene is the Organometallic compound with the formula Fe(C5H52 [3] The stability and volatility of the butane resulting from such deprotonation reactions is convenient, but can also be a problem for large-scale reactions because of the volume of a flammable gas produced. Butane, also called n -butane, is the unbranched Alkane with four Carbon Atoms CH3CH2CH2CH3 Deprotonation is a Chemistry term that refers to the removal of a Proton ( Hydrogen Cation H+ from a Molecule, forming
- LiC4H9 + R-H → C4H10 + R-Li
The kinetic basicity of n-BuLi is affected by the reaction solvent or cosolvent. Ligands that complex Li+ such as tetrahydrofuran (THF), tetramethylethylenediamine (TMEDA), hexamethylphosphoramide (HMPA), and 1,4-diazabicyclo[2. "THF" redirects here For other uses see THF (disambiguation. Tetramethylethylenediamine ( TMEDA or TEMED) is a Chemical compound with the formula (CH32NCH2CH2N(CH32 Hexamethylphosphoramide (abbreviated HMPA is a colorless organic liquid with the formula 3PO 2. 2]octane (DABCO) further polarize the Li-C bond and accelerate the metalation. DABCO or 14-diazabicyclooctane is a Chemical compound. It is used as a Catalyst, particularly in making Polyurethanes, and complexing Ligand Such additives can also aid in the isolation of the lithiated product, a famous example of which is dilithioferrocene.
- Fe(C5H5)2 + 2 LiC4H9 + 2 TMEDA → 2 C4H10 + Fe(C5H4Li)2(TMEDA)2
Schlosser's base is a superbase produced by treating butyllithium with potassium tert-butoxide. In Chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase but most chemists would accept An alkoxide is the Conjugate base of an Alcohol and therefore consists of an organic group bonded to a negatively charged Oxygen atom It is kinetically more reactive than butyllithium and is often used to accomplish difficult metalations. Metalation (metallation is a Chemical reaction which results in a Metal atom beingattached to a (usually organic) molecule The butoxide anion complexes the lithium and effectively produces butylpotassium, which is more reactive than the corresponding lithium reagent.
An example of the use of n-butyllithium as a base is the addition of an amide to methyl carbonate, where n-butyllithium serves to deprotonate the amine:
- n-BuLi + R2NH + (MeO)2CO → R2N-CO2Me + LiOMe + BuH
Halogen-lithium exchange
Butyllithium reacts with some organic bromides and iodides in an exchange reaction to form the corresponding organolithium derivative. The reaction usually fails with organic chlorides and fluorides:
- C4H9Li + RX → C4H9X + RLi (X = Br, I)
This reaction is a useful method for preparation of several types of RLi compounds, particularly aryllithium and some vinyllithium reagents. In the context of organic molecules aryl refers to any Functional group or Substituent derived from a Simple aromatic ring, may it be Phenyl A vinyl compound is any Organic compound that contains a vinyl group (also called ethenyl) &minus C[[Hydrogen H]] =CH sub>2 The utility of this method is significantly limited, however, by the presence in the reaction mixture of n-BuBr or n-BuI, which can react with the RLi reagent formed, and by competing dehydrohalogenation reactions, in which n-BuLi serves as a base:
- 2C4H9Br + RLi → C4H9R + LiBr
- 2C4H9Li + R'CH=CHBr → C4H10 + R'C≡CLi + LiBr
These side reaction are significantly less important for RI than for RBr, since the iodine-lithium exchange is several orders of magnitude faster than the bromine-lithium exchange. Dehydrohalogenation is an Organic chemistry reaction from which an Alkene is obtained from an Alkyl halide. For these reasons, aryl, vinyl and primary alkyl iodides are the preferred substrates, and t-BuLi rather than n-BuLi is usually used, since the formed t-BuI is immediately destroyed by the t-BuLi in a dehydrohalogenation reaction (thus requiring 2 equiv of t-BuLi). tert -Butyllithium is the Chemical compound with the formula (CH33CLi Alternatively, vinyl lithium reagents can be generated by direct reaction of the vinyl halide (e. g. cyclohexenyl chloride) with lithium or by tin-lithium exchange (see next section). [1]
Transmetalations
A related family of reactions are the transmetalations, wherein two organometallic compounds exchange their metals. Transmetalation (alt spelling transmetallation is a general Chemical reaction type in Organometallic chemistry describing the exchange of Ligands between Many examples of such reactions involve Li exchange with Sn:
- C4H9Li + Me3SnAr → C4H9SnMe3 + LiAr
- where Ar is aryl and Me is methyl
The tin-lithium exchange reactions have one major advantage over the halogen-lithium exchanges for the preparation of organolithium reagents, in that the product tin compounds (C4H9SnMe3 in the example above) are much less reactive towards lithium reagents than are the halide products of the corresponding halogen-lithium exchanges (C4H9Br or C4H9I). Tin is a Chemical element with the symbol Sn (stannum and Atomic number 50 Other metals and metaloids which undergo such exchange reactions are organic compounds of mercury, selenium, and tellurium. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across Metalloid is a term used in Chemistry when classifying the Chemical elements On the basis of their general physical and chemical properties nearly every element Organomercury refers to the group of organometallic compounds that contain mercury. Organoselenium compounds are Chemical compounds containing Carbon to Selenium Chemical bonds Organoselenium chemistry is the corresponding Tellurium (tɪˈlʊəriəm/ /tɛl- is a Chemical element that has the symbol Te and Atomic number 52
Carbonyl Additions
Organolithium reagents, including n-BuLi are used in synthesis of specific aldehydes and ketones. An aldehyde is an organic compound containing a terminal Carbonyl group. A ketone (pronounced as key tone) is either the Functional group characterized by a Carbonyl group (O=C linked to two other Carbon atoms or One such synthetic pathway is the reaction of an organolithium reagent with disubstituted amides:
- R1Li + R2CONMe2 → LiNMe2 + R2C(O)R1
Carbolithiations
Butyllithium will add to certain activated terminal alkenes, such as styrene, butadiene or even ethylene itself to form a new organolithium reagent. In Chemistry, an amide is one of three kinds of Compounds (sometimes called acid amide the organic Functional group characterized In Organic chemistry, an alkene, olefin, or olefine is an unsaturated Chemical compound containing at least one Carbon Styrene, also known as vinyl benzene as well as many other names (see table is an Organic compound with the Chemical formula C6H5CH=CH2 Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. This reaction is the basis for the commercially important use of butyllithium for the production of polystyrene and polybutadiene. Polystyrene ˌpɒliˈstaɪriːn ( IUPAC Polyphenylethene is an aromatic Polymer made from the aromatic Monomer Styrene Polybutadiene is a Synthetic rubber that is a Polymer formed from the Polymerization of the Monomer 13-butadiene.
- C4H9Li + CH2=CH-C6H5 → C4H9-CH2-CH(Li)-C6H5
Degradation of THF
THF is deprotonated by butyllithium, especially in the presence of TMEDA, by loss of one of four protons adjacent to oxygen. Tetramethylethylenediamine ( TMEDA or TEMED) is a Chemical compound with the formula (CH32NCH2CH2N(CH32 This process, which consumes butyllithium to generate butane, induces a reverse cycloaddition to give enolate of acetaldehyde and ethylene. A cycloaddition is a Pericyclic Chemical reaction, in which two π bonds are lost and two σ bonds are gained the resulting reaction is a Acetaldehyde, sometimes known as ethanal, is an organic chemical compound with the formula C[[Hydrogen H]]3CH O or MeCHO Structure This Hydrocarbon has four Hydrogen Atoms bound to a pair of Carbon atoms that are connected by a Double bond. Therefore, reactions of BuLi in THF are typically conducted at low temperatures, such as –78 °C, as is conveniently produced by a freezing bath of dry ice/acetone. Dry ice is solid Carbon dioxide. It is commonly used as a versatile cooling agent Higher temperatures (-25 °C or even -15 °C) are also used.
Thermal decomposition
When heated, n-BuLi, analogously to other alkyllithium reagents with "β-hydrogens", undergoes β-hydride elimination to produce an 1-butene and LiH:
- C4H9Li + Δ
LiH + CH3CH2CH=CH2
Safety
It is chemically sensible to store and handle all alkyl-lithiums in sealed systems under inert gas to prevent loss of activity and for reasons of safety. BuLi reacts violently with water:
- C4H9Li + H2O → C4H10 + LiOH
BuLi also reacts with CO2 to give lithium pentanoate:
- C4H9Li + CO2 → C4H9CO2Li
In particular tertiary-butyllithium is extremely reactive towards air and moisture, its hydrolysis being significantly exothermic enough to ignite the solvent (commercial sources typically using tetrahydrofuran, diethyl ether, or hexanes), and thus often inflaming upon exposure to the atmosphere. Lithium hydroxide (LiOH is a corrosive Alkali hydroxide. It is a white Hygroscopic Crystalline material In some instances it may self-seal, e. g. in needles, preventing further access of oxygen due to hydroxide and oxide barriers being formed. This is analogous to oxide surface layers on the perceived stable metallic form of aluminum. While t-BuLi is classified as being spontaneously pyrophoric in an air atmosphere, n-BuLi is not, but to prevent degradation is still handled under a dry nitrogen atmosphere.
References
- ^ a b c Brandsma, L. ; Verkraijsse, H. D. (1987). Preparative Polar Organometallic Chemistry I. Berlin: Springer-Verlag. Springer Science+Business Media or Springer (ˈʃpʁɪŋɐ is a worldwide Publishing company based in Germany, which publishes textbooks academic ISBN 3-540-16916-4.
- ^ Elschenbroich, C. ”Organometallics” (2006) Wiley-VCH: Weinheim. ISBN 978-3-29390-6
- ^ Sanders, R. ; Mueller-Westerhoff, U. T. (1996). "The Lithiation of Ferrocene and Ruthenocene - A Retraction and an Improvement". Journal of Organometallic Chemistry 512: 219-224. Journal of Organometallic Chemistry is published by Elsevier. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
Further reading
- ChemExper Chemical Directory
- FMC Lithium manufacturer's product sheets
- Environmental Chemistry directory
- Weissenbacher, Anderson, Ishikawa, Organometallics, July 1998, p681. 7002, Chemicals Economics Handbook SRI International
- HPV test plan, submitted by FMC Lithium to EPA
- Ovaska, T. V. e-EROS Encyclopedia of Reagents for Organic Synthesis "n-butyllithium. The Encyclopedia of Reagents for Organic Synthesis is published in print and online by John Wiley & Sons Ltd " Wiley and sons. 2006. doi:10.1002/047084289X.rb395
- Greenwood, N. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. N. ; Earnshaw, A. Chemistry of the Elements, 2nd ed. 1997: Butterworth-Heinemann, Boston.
External links
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