Salpn ligand

Salpn ligand
Names
	IUPAC name 2,2'-{1,2-Propanediylbis[nitrilo(E)methylylidene]}diphenol
Identifiers
CAS Number	257636-52-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	10296917 ;
ECHA InfoCard	100.002.159
UNII	7S023Y0W20 ;
CompTox Dashboard (EPA)	DTXSID2041200 ;
	InChI InChI=1S/C17H18N2O2/c1-13(19-12-15-7-3-5-9-17(15)21)10-18-11-14-6-2-4-8-16(14)20/h2-9,11-13,20-21H,10H2,1H3/b18-11+,19-12+ Key: RURPJGZXBHYNEM-GDAWTGGTSA-N;
	SMILES OC1=CC=CC=C1/C=N/CC(C)/N=C/C2=CC=CC=C2O;
Properties
Chemical formula	C17H18N2O2
Molar mass	282.343 g·mol−1
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). (what is ?) Infobox references

Salpn is the common name for a chelating ligand, properly called N,N′-bis(salicylidene)-1,2-propanediamine, used as a motor oil additive.^[1]

The molecular structure of pure (metal-free) salpn, sometimes denoted H₂(salpn) or salpnH₂, can be described as the salen ligand with a methyl group attached to the ethylene bridge.

As in the case of salen compound, the actual ligand is usually the conjugate base salpn²⁻
, the divalent anion that result from the metal-free compound by the loss of two hydroxyl protons. 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.^[2]

Preparation

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

2C₆H₄(OH)CHO + CH₃CH(NH₂)CH₂NH₂ → [C₆H₄(OH)CH]₂CH₃CHNCH₂N + 2H₂O

Uses

Salpn is used as a fuel additive as a metal deactivator 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 compounds with the metals, suppressing their catalytic activity.^[1] While salpn forms stable chelate complexes with many metals including copper, iron, chromium, and nickel, it is the coordination with copper that makes it a popular choice as a fuel additive. Copper has the highest catalytic activity in fuel, and salpn forms a highly stable square planar complex with the metal.^[3]

Salpn is preferred over salen, possibly because it has higher solubility in non-polar liquids.

References

^ ^a ^b Dabelstein, W.; Reglitzky A.; Schutze A.; Reders, K. "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. ISBN 978-3527306732.
^ 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. doi:10.1021/ic971592y
^ Evans, D. A.; Miller, S. J.; Lectka, T.; von Matt. P. (1999). "Chiral Bis(oxazoline)copper(II) Complexes as Lewis Acid Catalysts for Enantioselective Diels-Alder Reaction". J. Am. Chem. Soc. 121: 7559–7573. doi:10.1021/ja991190k.

[ullmann-1] Dabelstein, W.; Reglitzky A.; Schutze A.; Reders, K. "Automotive Fuels". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. ISBN 978-3527306732.

[reddy-2] 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. doi:10.1021/ic971592y

[3] Evans, D. A.; Miller, S. J.; Lectka, T.; von Matt. P. (1999). "Chiral Bis(oxazoline)copper(II) Complexes as Lewis Acid Catalysts for Enantioselective Diels-Alder Reaction". J. Am. Chem. Soc. 121: 7559–7573. doi:10.1021/ja991190k.

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