Pentaethylenehexamine (abbreviated PEHA) is an organic

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

. It is composed of five ethylene groups -CH₂CH₂- joined together in a chain by four secondary amine groups (-NH-) and terminated on each end by primary amine groups (-NH₂). Pentaethylenehexamine is a hexadentate ligand, owing to the Lewis basicity of the six amine groups. Pentaethylenehexamine is in the category of polyethyleneamines and is part of mixtures of these sold commercially. Commercial supplies of pentaethylenehexamine contain, in addition to the linear form, branched and cyclic

polyamine A polyamine is an organic compound having two or more amino groups. Alkyl polyamines occur naturally, but some are synthetic. Alkylpolyamines are colorless, hygroscopic, and water soluble. Near neutral pH, they exist as the ammonium derivatives. ...

s. As an amine, it is an

organic base An organic base is an organic compound which acts as a base. Organic bases are usually, but not always, proton acceptors. They usually contain nitrogen atoms, which can easily be protonated. For example, amines or nitrogen-containing heterocyclic ...

and can form

ammonium salt Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) molecular ion with the chemical formula or . It is formed by the addition of a proton (a hydrogen nucleus) to ammonia (). Ammonium i ...

s by reaction with various acids. Salts with counter-

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

s such as

chloride The term chloride refers to a compound or molecule that contains either a chlorine anion (), which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond (). The pr ...

sulfate The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

, naphthalene-2-sulfonate, and tosylate. Tosylate salts can be used to separate the linear molecule from the other forms, as it is less soluble.

Properties

The

infrared spectrum Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...

of pentaethylenehexamine salts show characteristics of the ammonium present. It has stretching modes, asymmetric and symmetric bending modes, but most useful absorption bands are due to rocking mode, where -NH₃⁺ is at 810 cm⁻¹ and -NH₂⁺- is at 768 cm⁻¹.

Reactions

Pentaethylenehexamine undergoes an Eschweiler–Clarke reaction with

formaldehyde Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...

and

formic acid Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid. It has the chemical formula HCOOH and structure . This acid is an important intermediate in chemical synthesis and occurs naturally, most notably in some an ...

to substitute all of the amine hydrogen atoms with

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated a ...

s, giving octamethylpentaethylenehexamine (OMPEHA). Pentaethylenehexamine can rearrange to form ''N'',''N''′-bis(2-aminoethyl)piperazine-1,4-diethylamine.

Ligand

As a

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

pentaethylenehexamine is abbreviated peha or PEHA. It is a strong field ligand. It can coordinate cobalt, nickel, copper, zinc, cadmium

lanthanum Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...

, neodymium,

europium Europium is a chemical element; it has symbol Eu and atomic number 63. It is a silvery-white metal of the lanthanide series that reacts readily with air to form a dark oxide coating. Europium is the most chemically reactive, least dense, and soft ...

samarium Samarium is a chemical element; it has symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of s ...

, lead, thorium, or uranium.

Use

Pentaethylenehexamine is used in

ion exchange resin An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange, that is also known as an ionex. It is an solubility, insoluble matrix (or support structure) normally in the form of small (0.25–1.43&nbs ...

s, eg Lewatit 6718 HLH. Pentaethylenehexamine has been investigated as a component in carbon dioxide capture, including direct from the air for conversion to

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...

References

{{Reflist Ethyleneamines Hexadentate ligands Secondary amines