Lindlar catalyst: Structure, CAS Number, Properties and Uses

Lindlar catalyst (CAS 53092-86-7) is palladium metal, about 5% by weight, deposited on calcium carbonate and poisoned with lead, used to stop hydrogenation at the alkene instead of running it through to the alkane. Chemists use it to turn a carbon-carbon triple bond into a single, controlled cis double bond, a selectivity ordinary hydrogenation catalysts cannot match. Its mechanism, composition, manufacture, commercial forms and hazard classification follow below.

What Is Lindlar Catalyst?#

Lindlar catalyst is a heterogeneous palladium catalyst, not a single molecular compound, so it carries a mixture-level CAS number rather than a formula. ChemicalBook, cross-checked against TCI America, Oakwood Chemical and Colonial Metals, lists CAS 53092-86-7 for the standard grade; no independent second source has confirmed that number, so it is treated as single-source data. Some supplier listings instead cite CAS 7440-05-3, the registry number for elemental palladium metal, for the catalyst's active component; that number identifies the palladium itself, not the finished Pd-on-calcium-carbonate mixture, the same distinction the site draws for every supported PGM catalyst. Lindlar catalyst is one of the platinum group metal compounds and catalysts cataloged with a dedicated CAS registry entry on this site.

The active metal is palladium deposited on a calcium carbonate support, occasionally barium carbonate, and deliberately poisoned with lead to blunt its reactivity. Palladium, platinum group metal element 46, is the PGM used this way for alkyne semi-hydrogenation, covered further under Uses, below. Calcium carbonate alone has no catalytic activity, so "Lindlar catalyst" refers to the full poisoned Pd-on-CaCO3 system, never to the carbonate by itself.

How Lindlar Catalyst Reduces Alkynes to Cis-Alkenes#

Lindlar catalyst reduces a carbon-carbon triple bond to a cis double bond by adsorbing the alkyne on the palladium surface and delivering both hydrogen atoms from the same face, a mechanism chemists call syn addition. Three linked steps carry out the reaction.

1. Adsorb the alkyne substrate and dissociated hydrogen atoms onto adjacent palladium sites.
2. Deliver both hydrogen atoms to the same face of the triple bond, forming a surface-bound alkene.
3. Desorb the alkene product before it can readsorb for a second round of hydrogenation.

That third step works only because the remaining active sites are scarce, a direct consequence of the lead poisoning described next.

Why Lead and Quinoline Poisoning Stop the Reaction at the Alkene#

Lead poisoning stops the reaction at the alkene because lead deposits on a fraction of the palladium surface sites and blocks them, the same site-blocking mechanism documented for lead as an unwanted autocatalyst poison, here used deliberately. In automotive catalysis, lead from tetraethyl-lead fuel additive deposits on PGM surfaces as an oxide, sulfate or halide and irreversibly destroys converter activity, a problem serious enough that leaded gasoline was phased out. Lindlar catalyst repurposes that same chemistry as a design feature: a controlled, partial lead loading, standardly added as lead acetate during manufacture, slows the second hydrogenation step (alkene to alkane) far more than the first (alkyne to alkene), so the reaction stalls cleanly at the alkene. Quinoline, where the grade calls for it, adsorbs reversibly on the remaining active sites and suppresses over-reduction to the alkane further still, according to Wikipedia's account of the standard preparation.

Cis vs Trans: Why the Product Is Always the Cis-Alkene#

Lindlar catalyst gives the cis-alkene exclusively because syn addition delivers both hydrogens to one face of the former triple bond, unlike sodium-in-ammonia reduction, which gives the trans-alkene. Both hydrogen atoms bond to the substrate from the same side of the palladium surface, so the two new carbon-hydrogen bonds end up on the same side of the resulting double bond, locking in the cis geometry. Dissolving-metal reduction with sodium in liquid ammonia proceeds through a completely different, radical-anion mechanism that favors the more stable trans-alkene instead, and organic chemists choose between the two methods based on which geometry the target molecule requires.

PGM Content and Composition#

Lindlar catalyst's standard grade carries about 5 wt% palladium, within the 1 to 10 wt% range typical of supported Pd/C-family catalysts, of which 5% and 10% are the two most common loadings. That range applies across the whole family of carbon- and carbonate-supported palladium catalysts used in hydrogenation chemistry, not to Lindlar catalyst alone, so its 5% loading is a mainstream choice rather than a special number. The lead component typically runs around 3.5% by weight, supplied as lead acetate or lead oxide during manufacture, and quinoline, where used, is a separate additive rather than a fixed component of the catalyst itself; because the mixture is not a stoichiometric compound, no single Pd weight-percent can be computed from a molecular formula the way it can for a discrete salt. Lindlar catalyst sits alongside the site's broader coverage of palladium compounds, most of which are discrete molecular species rather than a supported mixture like this one.

Physical and Chemical Properties#

Lindlar catalyst has no single melting point, density or molecular weight because it is a supported mixture, not a discrete compound. Its appearance is established at the supplier level instead: Sigma-Aldrich's safety data sheet for product 62145 describes the standard grade as a dark grey powder with lumps, while ChemicalBook separately describes it as light brown to dark brownish-grey, a range the two sources attribute to normal lot-to-lot and supplier variation rather than a single reference color. What holds across grades is behavior common to supported-metal heterogeneous catalysts generally: an insoluble solid that does not dissolve in water or common organic solvents, since the active metal is physically deposited on, rather than chemically bonded within, the support. Suppliers store the catalyst in an inert atmosphere at room temperature, per ChemicalBook, or in a tightly closed container in a dry, well-ventilated place, per the Sigma-Aldrich SDS.

How Lindlar Catalyst Is Made#

Lindlar catalyst is made by reducing palladium chloride onto a calcium carbonate (or barium carbonate) support, then adding a lead salt such as lead acetate or lead oxide as the poison.

1. Suspend a palladium(II) chloride precursor in a slurry with the calcium carbonate (or barium carbonate) support.
2. Reduce the palladium onto the support, depositing metallic palladium at roughly 5 wt% of the finished catalyst.
3. Add lead acetate, the standard poison salt, to deactivate a controlled fraction of the palladium surface sites.
4. Blend in quinoline, where the grade calls for it, as an added moderator that further suppresses over-reduction to the alkane.

This route, precipitating palladium onto a carbonate support and poisoning it with lead, is the standard preparation Wikipedia documents for the catalyst.

What Is Lindlar Catalyst Used For?#

Lindlar catalyst is used for selective semi-hydrogenation of alkynes to cis-alkenes, historically in the industrial synthesis of vitamin A and dihydrovitamin K1. Its selectivity makes it the default choice whenever a synthesis route needs to stop precisely at the alkene stage of a longer reduction sequence, a requirement that comes up repeatedly in fine-chemical and pharmaceutical manufacturing as well as in undergraduate organic chemistry laboratories. A frequently cited textbook example of that substrate scope is the semi-hydrogenation of phenylacetylene to styrene, which stops at the alkene stage without over-reducing it to ethylbenzene, per Wikipedia's alkyne article. No quantitative catalyst-loading or turnover-frequency data for Lindlar-catalyzed hydrogenations was found in the literature checked for this page, a genuine gap in the published record for this heterogeneous mixture rather than an omission on the site's part.

Vitamin A and Vitamin K1 Synthesis#

Vitamin A synthesis historically used Lindlar catalyst to install a cis double bond partway through the retinol chain without over-reducing it to the saturated chain. The same selective semi-hydrogenation step appears in the industrial route to dihydrovitamin K1, where an over-reduced product would lose the target molecule's biological activity. Both applications rely on the same property: the catalyst stops cleanly at the alkene stage even with excess hydrogen gas present.

Where Lindlar Catalyst Sits Among PGM Hydrogenation Catalysts#

Among the platinum group metals, palladium is the metal used for alkyne semi-hydrogenation, while platinum handles aromatic-ring and carbonyl hydrogenation, rhodium arene hydrogenation, and ruthenium carbonyl and carbohydrate hydrogenation. That division of labor across the six PGMs is not arbitrary: each metal's surface chemistry favors a different substrate class, which is why a chemist choosing a hydrogenation catalyst starts from the substrate rather than defaulting to one metal. Palladium's role in alkyne semi-hydrogenation and nitro-group reduction sits alongside the broader family of PGM catalysts in chemistry used across industrial and laboratory reactors, of which Lindlar catalyst is one specialized, deliberately poisoned member.

Commercial Forms, Purity and Price#

Lindlar catalyst is sold as a lead-poisoned or quinoline-poisoned 5% Pd on calcium carbonate powder, in laboratory gram-scale pack sizes rather than bulk industrial quantities. Johnson Matthey markets a family of Pd on calcium carbonate (Lindlar-type) catalysts customized per application, with quinoline supplied pre-added or sold separately as a moderator. A survey of current supplier catalogs also lists the standard grade as available from Sigma-Aldrich, TCI, Oakwood Chemical, Colonial Metals and Fluorochem, alongside Johnson Matthey's customizable family. Because the catalyst is roughly 5% palladium by weight, its cost tracks the palladium price more closely than a flat per-gram catalog rate, though suppliers price finished catalyst by the gram, not against contained-metal value.

Safety and Hazard Classification#

PubChem's C&L notification mirror records no signal word and no H-codes for the mixture-level CAS 53092-86-7, a gap in the registered classification rather than a claim about the lead content's hazard. At least one primary supplier safety data sheet, Sigma-Aldrich's SDS for product 62145 (revised 25 June 2014), independently classifies the finished catalyst overall as not a hazardous substance or mixture under GHS, with no pictogram or H-codes on its label, Hazard Material Identification System and National Fire Protection Association ratings of 0/0/0, and no OSHA, ACGIH or NIOSH occupational exposure limit listed for the product. That GHS classification sits alongside a separate transport classification driven by the lead content: the same SDS lists Lindlar catalyst under UN 2291, Hazard Class 6.1, Packing Group III, proper shipping name "Lead compounds, soluble, n.o.s. (Lindlar Catalyst)," across the DOT, IMDG and IATA modes. The same document lists the product as not classified as a carcinogen by IARC, ACGIH, NTP or OSHA, and not a California Proposition 65 substance. REACH registration status and CLP classification specific to this mixture-level CAS are not established in the sources checked for this page. Laboratories handle the powder under standard precautions for a lead-bearing solid: gloves, fume-hood practice and avoiding dust inhalation.

Where Lindlar Catalyst Chemistry Stops: Vitamin Dosing and Health Claims#

This page covers Lindlar catalyst's chemistry only; it does not give vitamin A or vitamin K1 dosing, supplementation or health-claim information, which sits outside a PGM reference site. Its role in vitamin A manufacturing is a synthesis-chemistry fact, not a basis for supplement guidance; readers seeking dosing or clinical information should consult a medical source instead.

Related PGM Hydrogenation Catalysts#

Lindlar catalyst belongs to a small family of named PGM hydrogenation catalysts, three of which are covered on this site: Pearlman's catalyst, Wilkinson's catalyst and Crabtree's catalyst. Each one occupies a different niche of hydrogenation chemistry, heterogeneous or homogeneous, defined by its metal center and its substrate scope.

History#

Herbert Lindlar developed the catalyst in 1952, publishing the method as "Ein neuer Katalysator für selektive Hydrierungen" in Helvetica Chimica Acta, volume 35, issue 2, pages 446 to 450, per the citation Wikipedia records for the original paper. Its use in early vitamin A manufacturing spread its name into standard organic-chemistry vocabulary. The catalyst's employer or sponsoring institution at the time is not independently confirmed in the sources checked for this page, so it is not stated here.

Frequently Asked Questions#

What is the formula of Lindlar's catalyst? Lindlar's catalyst has no single molecular formula because it is a heterogeneous mixture, palladium (about 5 wt%) on calcium carbonate, poisoned with lead. Suppliers and databases record it under the mixture-level CAS 53092-86-7 instead.

What does Lindlar's catalyst do? Lindlar's catalyst selectively hydrogenates a carbon-carbon triple bond to a cis double bond and then stops, rather than reducing the product further to the saturated alkane. That stopping point is why chemists choose it for alkyne-to-alkene conversions.

What happens when an alkyne reacts with hydrogen over Lindlar's catalyst? An alkyne reacting with hydrogen over Lindlar's catalyst gives the cis-alkene through syn addition, both hydrogen atoms bonding to the same face of the former triple bond. Lead poisoning stops the reaction there, before it reaches the alkane.

What is the difference between Lindlar's catalyst and Wilkinson's catalyst? Lindlar's catalyst is a heterogeneous, lead-poisoned palladium solid for alkyne semi-hydrogenation, while Wilkinson's catalyst is a homogeneous, dissolved rhodium complex, RhCl(PPh3)3, for simple alkene hydrogenation. They hydrogenate different substrates through different mechanisms.

Is Lindlar's catalyst still used industrially today? Yes. Lindlar's catalyst remains in use for fine-chemical-scale alkyne semi-hydrogenation, and suppliers including Sigma-Aldrich, Johnson Matthey and several other specialty chemical houses still market Pd-on-calcium-carbonate catalyst families built on the poisoning principle Herbert Lindlar introduced in 1952.

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