Resorcinarene
Encyclopedia
A resorcinarene is a macrocycle
, or a cyclic
oligomer
, based on the condensation of resorcinol
(1,3-dihydroxybenzene) and an aldehyde
. Resorcinarenes are a type of calixarene
.
and an aldehyde
in concentrated acid
solution. Recrystallization typically gives the desired isomer in quite pure form. However, for certain aldehydes, the reaction conditions lead to significant by-product
s. Therefore, alternative condensation conditions have been developed, including the use of Lewis acid
catalysts.
A green chemistry
procedure was recently developed using solvent-free conditions: resorcinol, an aldehyde, and p-toluenesulfonic acid
are ground together in a mortar and pestle
at low temperature.A paste-like solid forms upon sitting for several minutes, which can be washed with water and crystallized to give the desired resorcinarene.
Under each of these conditions, aromatic aldehydes react much faster, but less stereoselectively than aliphatic aldehydes, and the reaction frequently leads to a mixture of desired and undesired products.
groups that can participate in hydrogen bonding interactions. Depending on the aldehyde starting material, the lower rim includes four appending groups, usually chosen to give optimal soubility.
The resorcin[n]arene nomenclature
is analogous to that of calix[n]arenes, in which 'n' represents the number of repeating units in the ring. Pyrogallolarenes are related macrocycles derived from the condensation of pyrogallol
(1,2,3-trihydroxybenzene) with an aldehyde.
noted that the condensation reaction of resorcinol
and benzaldehyde
gave a mixture of products that was beyond the characterization methods of that time. Over the following century, the product mixture was more fully characterized by X-ray crystallography
and Nuclear Magnetic Resonance
and found to include general structure shown above and several other stereoisomers.
first noted the potential for resorcinarenes to interact with other molecules as a host-guest complex.
It was later found that resorcinarenes and pyrogallolarenes self-assemble
into to larger supramolecular structures. Both in the crystalline state and in organic solvents, six resorcinarene molecules are known to form hexamers with an internal volume of around one cubic nanometer (nanocapsules) and shapes similar to the Archimedean solid
s. Hydrogen bonds appear to hold the assembly together. A number of solvent or other molecules reside inside.
The resorcinarene is also the basic structural unit for other molecular recognition scaffolds. A number of chemists, including Nobel-laureate
Donald J. Cram
, constructed novel molecular structures based on this macrocycle, namely cavitand
s and carcerand
s.
Macrocycle
A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of nine or more atoms to be a macrocycle...
, or a cyclic
Cyclic compound
In chemistry, a cyclic compound is a compound in which a series of atoms is connected to form a loop or ring.While the vast majority of cyclic compounds are organic, a few inorganic substances form cyclic compounds as well, including sulfur, silanes, phosphanes, phosphoric acid, and triboric acid. ...
oligomer
Oligomer
In chemistry, an oligomer is a molecule that consists of a few monomer units , in contrast to a polymer that, at least in principle, consists of an unlimited number of monomers. Dimers, trimers, and tetramers are oligomers. Many oils are oligomeric, such as liquid paraffin...
, based on the condensation of resorcinol
Resorcinol
Resorcinol is a dihydroxy benzene. It is the 1,3-isomer of benzenediol with the formula C6H42.-Nomenclature:Benzene-1,3-diol is the name recommended by the International Union of Pure and Applied Chemistry in its 1993 Recommendations for the Nomenclature of Organic Chemistry.-Production:It is...
(1,3-dihydroxybenzene) and an aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
. Resorcinarenes are a type of calixarene
Calixarene
A calixarene is a macrocycle or cyclic oligomer based on a hydroxyalkylation product of a phenol and an aldehyde. The word calixarene is derived from calix or chalice because this type of molecule resembles a vase and from the word arene that refers to the aromatic building block...
.
Synthesis
The resorcinarene macrocycle is typically prepared by condensation of resorcinolResorcinol
Resorcinol is a dihydroxy benzene. It is the 1,3-isomer of benzenediol with the formula C6H42.-Nomenclature:Benzene-1,3-diol is the name recommended by the International Union of Pure and Applied Chemistry in its 1993 Recommendations for the Nomenclature of Organic Chemistry.-Production:It is...
and an aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
in concentrated acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
solution. Recrystallization typically gives the desired isomer in quite pure form. However, for certain aldehydes, the reaction conditions lead to significant by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....
s. Therefore, alternative condensation conditions have been developed, including the use of Lewis acid
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
catalysts.
Green chemistry
Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances...
procedure was recently developed using solvent-free conditions: resorcinol, an aldehyde, and p-toluenesulfonic acid
P-Toluenesulfonic acid
p-Toluenesulfonic acid or tosylic acid is an organic compound with the formula CH3C6H4SO3H. It is a white solid that is soluble in water, alcohols, and other polar organic solvents. The 4-CH3C6H4SO2- group is known as the Tosyl group and is often abbreviated as Ts or Tos...
are ground together in a mortar and pestle
Mortar and pestle
A mortar and pestle is a tool used to crush, grind, and mix solid substances . The pestle is a heavy bat-shaped object, the end of which is used for crushing and grinding. The mortar is a bowl, typically made of hard wood, ceramic or stone...
at low temperature.A paste-like solid forms upon sitting for several minutes, which can be washed with water and crystallized to give the desired resorcinarene.
Under each of these conditions, aromatic aldehydes react much faster, but less stereoselectively than aliphatic aldehydes, and the reaction frequently leads to a mixture of desired and undesired products.
Structure
Resorcinarenes can be characterized by a wide upper rim and a narrow lower rim. The upper rim includes eight hydroxylHydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
groups that can participate in hydrogen bonding interactions. Depending on the aldehyde starting material, the lower rim includes four appending groups, usually chosen to give optimal soubility.
The resorcin[n]arene nomenclature
IUPAC nomenclature
A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry ....
is analogous to that of calix[n]arenes, in which 'n' represents the number of repeating units in the ring. Pyrogallolarenes are related macrocycles derived from the condensation of pyrogallol
Pyrogallol
Pyrogallol or benzene-1,2,3-triol is a benzenetriol. It is a white crystalline powder and a powerful reducing agent. It was first prepared by Scheele 1786 by heating gallic acid. An alternate preparation is heating para-chlorophenoldisulphonic acid with potassium hydroxide.When in alkaline...
(1,2,3-trihydroxybenzene) with an aldehyde.
History
During the late 19th century, Adolf von BaeyerAdolf von Baeyer
Johann Friedrich Wilhelm Adolf von Baeyer was a German chemist who synthesized indigo, and was the 1905 recipient of the Nobel Prize in Chemistry. Born in Berlin, he initially studied mathematics and physics at Berlin University before moving to Heidelberg to study chemistry with Robert Bunsen...
noted that the condensation reaction of resorcinol
Resorcinol
Resorcinol is a dihydroxy benzene. It is the 1,3-isomer of benzenediol with the formula C6H42.-Nomenclature:Benzene-1,3-diol is the name recommended by the International Union of Pure and Applied Chemistry in its 1993 Recommendations for the Nomenclature of Organic Chemistry.-Production:It is...
and benzaldehyde
Benzaldehyde
Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. This colorless liquid has a characteristic pleasant almond-like odor...
gave a mixture of products that was beyond the characterization methods of that time. Over the following century, the product mixture was more fully characterized by X-ray crystallography
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
and Nuclear Magnetic Resonance
Nuclear magnetic resonance
Nuclear magnetic resonance is a physical phenomenon in which magnetic nuclei in a magnetic field absorb and re-emit electromagnetic radiation...
and found to include general structure shown above and several other stereoisomers.
Supramolecular Chemistry
Yasuhiro Aoyama's research group at Kyoto UniversityKyoto University
, or is a national university located in Kyoto, Japan. It is the second oldest Japanese university, and formerly one of Japan's Imperial Universities.- History :...
first noted the potential for resorcinarenes to interact with other molecules as a host-guest complex.
It was later found that resorcinarenes and pyrogallolarenes self-assemble
Molecular self-assembly
Molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...
into to larger supramolecular structures. Both in the crystalline state and in organic solvents, six resorcinarene molecules are known to form hexamers with an internal volume of around one cubic nanometer (nanocapsules) and shapes similar to the Archimedean solid
Archimedean solid
In geometry an Archimedean solid is a highly symmetric, semi-regular convex polyhedron composed of two or more types of regular polygons meeting in identical vertices...
s. Hydrogen bonds appear to hold the assembly together. A number of solvent or other molecules reside inside.
The resorcinarene is also the basic structural unit for other molecular recognition scaffolds. A number of chemists, including Nobel-laureate
Nobel Prize
The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...
Donald J. Cram
Donald J. Cram
Donald James Cram was an American chemist who shared the 1987 Nobel Prize in Chemistry with Jean-Marie Lehn and Charles J...
, constructed novel molecular structures based on this macrocycle, namely cavitand
Cavitand
A cavitand is a container shaped molecule. The cavity of the cavitand allows it to engage in host-guest chemistry with guest molecules of a complementary shape and size. Examples include cyclodextrins, calixarenes, pillararenes and cucurbiturils....
s and carcerand
Carcerand
A carcerand is a host molecule that completely entraps its guest so that it will not escape even at high temperatures. This type of molecule was first described by Donald J. Cram in 1985 and is derived from the Latin carcer, or prison...
s.