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1,8-Bis(dimethylamino)naphthalene
Encyclopedia
1,8-Bisnaphthalene is a chemical compound that was first prepared in 1968 by Roger Alder
FRS at the University of Bristol
. It is often referred by the trade name Proton Sponge, a trademark of Sigma-Aldrich
. This compound is a diamine
in which the two dimethylamino groups are attached on the same side or peri position
of a naphthalene
system. Proton-sponge has several very interesting properties; one is its very high basicity
; another is its spectroscopic properties.
of 12.1 for its conjugate acid
in aqueous solution, 1,8-bis(dimethylamino)naphthalene is one of the strongest amine
bases known, although it only absorbs proton
s slowly—hence the trade name. The high basicity is attributed to the relief of strain upon protonation
and/or the strong interaction between the nitrogen
lone pair
s. However, the molecule is sterically hindered
, making it a weak nucleophile
. Because of this combination of properties, it has been used in organic synthesis as a highly selective non-nucleophilic base.
The spectroscopic properties of Proton-sponge are very interesting for researchers of molecular chemistry and have been researched for a long time. Proton-sponge emits a double fluorescence
in various solutions due to the mixture of two ground-state species.
of 1,8-diaminonaphthalene
with iodomethane
or dimethyl sulfate
.
. The pKa of trimethylated Proton-sponge is 6.43 in aqueous solution.
by reaction with tris(dimethylamino)bromophosphonium bromide in the presence of triethylamine
. HMPN has a pKBH+ of 29.9 in acetonitrile
which is more than 11 orders of magnitude higher than Proton Sponge.
Roger Alder
Roger William Alder, FRS is an Emeritus Professor of organic chemistry at the University of Bristol.His research involves the study of novel compounds with unusual properties, such as proton sponges and stable carbenes.-External links:*...
FRS at the University of Bristol
University of Bristol
The University of Bristol is a public research university located in Bristol, United Kingdom. One of the so-called "red brick" universities, it received its Royal Charter in 1909, although its predecessor institution, University College, Bristol, had been in existence since 1876.The University is...
. It is often referred by the trade name Proton Sponge, a trademark of Sigma-Aldrich
Sigma-Aldrich
Sigma-Aldrich Corporation , is a life science and high technology company with over 7,600 employees and operations in 40 countries. Its chemical and biochemical products and kits are used in scientific research, biotechnology, pharmaceutical development, the diagnosis of disease, and as key...
. This compound is a diamine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
in which the two dimethylamino groups are attached on the same side or peri position
Arene substitution patterns
Arene substitution patterns are part of organic chemistry IUPAC nomenclature and pinpoint the position of substituents other than hydrogen in relation to each other on an aromatic hydrocarbon.- Ortho, meta, and para substitution :...
of a naphthalene
Naphthalene
Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...
system. Proton-sponge has several very interesting properties; one is its very high basicity
Acid-base reaction theories
An acid–base reaction is a chemical reaction that occurs between an acid and a base. Several concepts that provide alternative definitions for the reaction mechanisms involved and their application in solving related problems exist...
; another is its spectroscopic properties.
Structure and properties
With a pKaAcid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid-base reactions...
of 12.1 for its conjugate acid
Conjugate acid
Within the Brønsted–Lowry acid-base theory , a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward chemical...
in aqueous solution, 1,8-bis(dimethylamino)naphthalene is one of the strongest amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
bases known, although it only absorbs proton
Proton
The proton is a subatomic particle with the symbol or and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number....
s slowly—hence the trade name. The high basicity is attributed to the relief of strain upon protonation
Protonation
In chemistry, protonation is the addition of a proton to an atom, molecule, or ion. Some classic examples include*the protonation of water by sulfuric acid:*the protonation of isobutene in the formation of a carbocation:2C=CH2 + HBF4 → 3C+ + BF4−*the protonation of ammonia in the...
and/or the strong interaction between the nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
lone pair
Lone pair
In chemistry, a lone pair is a valence electron pair without bonding or sharing with other atoms. They are found in the outermost electron shell of an atom, so lone pairs are a subset of a molecule's valence electrons...
s. However, the molecule is sterically hindered
Steric effects
Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds , and this may affect the molecule's preferred shape and reactivity.-Steric...
, making it a weak nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
. Because of this combination of properties, it has been used in organic synthesis as a highly selective non-nucleophilic base.
The spectroscopic properties of Proton-sponge are very interesting for researchers of molecular chemistry and have been researched for a long time. Proton-sponge emits a double fluorescence
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
in various solutions due to the mixture of two ground-state species.
Preparation
This compound is commercially available; it may be prepared by the methylationMethylation
In the chemical sciences, methylation denotes the addition of a methyl group to a substrate or the substitution of an atom or group by a methyl group. Methylation is a form of alkylation with, to be specific, a methyl group, rather than a larger carbon chain, replacing a hydrogen atom...
of 1,8-diaminonaphthalene
1,8-Diaminonaphthalene
1,8-Diaminonaphthalene is an aromatic amine. It is a precursor to 1,8-bisnaphthalene....
with iodomethane
Iodomethane
Methyl iodide, also called iodomethane, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hydrogen atom by an atom of iodine. It is naturally...
or dimethyl sulfate
Dimethyl sulfate
Dimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...
.
Reactions
Proton-sponge is methylated by using dimethyl sulfateDimethyl sulfate
Dimethyl sulfate is a chemical compound with formula 2SO2. As the diester of methanol and sulfuric acid, its formula is often written as 2SO4 or even Me2SO4, where CH3 or Me is methyl...
. The pKa of trimethylated Proton-sponge is 6.43 in aqueous solution.
Other proton sponges
Second generation proton sponges are known with even higher basicity. 1,8-bis(hexamethyltriaminophosphazenyl)naphthalene or HMPN is prepared from 1,8-diaminonaphthalene1,8-Diaminonaphthalene
1,8-Diaminonaphthalene is an aromatic amine. It is a precursor to 1,8-bisnaphthalene....
by reaction with tris(dimethylamino)bromophosphonium bromide in the presence of triethylamine
Triethylamine
Triethylamine is the chemical compound with the formula N3, commonly abbreviated Et3N. It is also abbreviated TEA, yet this abbreviation must be used carefully to avoid confusion with triethanolamine, for which TEA is also a common abbreviation....
. HMPN has a pKBH+ of 29.9 in acetonitrile
Acetonitrile
Acetonitrile is the chemical compound with formula . This colourless liquid is the simplest organic nitrile. It is produced mainly as a byproduct of acrylonitrile manufacture...
which is more than 11 orders of magnitude higher than Proton Sponge.