} Salpn is the common name for a

chelating Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a Denticity, polydentate (multiple bonded) ligand and a single central metal atom. These l ...

ligand In coordination chemistry, a ligand is an ion or molecule (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 electr ...

, properly called ''N'',''N''-bis(salicylidene)-1,2-propanediamine, used as a

motor oil Motor oil, engine oil, or engine lubricant is any one of various substances used for the lubrication of internal combustion engines. They typically consist of base oils enhanced with various additives, particularly antiwear additives, deterg ...

additive. The molecular structure of pure (metal-free) salpn, sometimes denoted H₂(salpn) or salpnH₂, can be described as the

salen ligand Salen refers to a tetradentate C2-symmetric ligand synthesized from salicylaldehyde (sal) and ethylenediamine (en). It may also refer to a class of compounds, which are structurally related to the classical salen ligand, primarily bis-Schiff base ...

with a

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 . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...

attached to the ethylene bridge that links the two nitrogen atoms. As in the case of salen compound, the actual ligand is usually the

conjugate base A conjugate acid, within the Brønsted–Lowry acid–base theory, is a chemical compound formed when an acid donates a proton () to a base—in other words, it is a base with a hydrogen ion added to it, as in the reverse reaction it loses a ...

salpn^2-, the

divalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of an ...

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 convent ...

that result from the metal-free compound by the loss of two

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

s. This dianion is commonly denoted "(salpn)" in formulas of metal complexes. The abbreviation "salpn" is also sometimes used for the structural isomer ''N'',''N''-bis(salicylidene)-1,3-diaminopropane and its conjugate base,K. Rajender Reddy, M. V. Rajasekharan, and J.-P. Tuchagues (1998): "Synthesis, Structure, and Magnetic Properties of Mn(salpn)N₃, a Helical Polymer, and Fe(salpn)N₃, a Ferromagnetically Coupled Dimer(salpnH₂ = ''N'',''N''-bis(Salicylidene)-1,3-diaminopropane)". ''Inorganic Chemistry'', volume 37, issue 23, pages 5978–5982. derived from 1,3-diaminopropane rather than 1,2-diaminopropane.

Preparation

The synthesis of salpn is achieved by a condensation reaction of 1,2-diaminopropane with

salicylaldehyde Salicylic aldehyde (2-hydroxybenzaldehyde) is the organic compound with the formula (C7 H6 O2) C6H4CHO-2-OH. Along with 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde, it is one of the three isomers of hydroxybenzaldehyde. This colorless oil ...

: :2C₆H₄(OH)CHO + CH₃CH(NH₂)CH₂NH₂ → ₆H₄(OH)CHsub>2CH₃CHNCH₂N + 2H₂O

Uses

Salpn is used as a fuel additive as a

metal deactivator Metal deactivators, or metal deactivating agents (MDA) are fuel additives and oil additives used to stabilize fluids by deactivating (usually by sequestering) metal ions, mostly introduced by the action of naturally occurring acids in the fuel a ...

in motor oils. Trace metals degrade the fuels by catalyzing oxidation processes that lead to gums and solids. Metal deactivators like salpn form stable

coordination compound A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...

s with the metals, suppressing their catalytic activity. While salpn forms stable chelate complexes with many metals including

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

, and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

, it is the coordination with copper that makes it a popular choice as a fuel additive. Copper has the highest

catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

activity in fuel, and salpn forms a highly stable

square planar The square planar molecular geometry in chemistry describes the stereochemistry (spatial arrangement of atoms) that is adopted by certain chemical compounds. As the name suggests, molecules of this geometry have their atoms positioned at the corne ...

complex with the metal. Salpn is preferred over salen, possibly because it has higher solubility in

non-polar In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more pola ...

liquids.

References

{{reflist Schiff bases Phenols Tetradentate ligands