Stabilization of metal carbonyls
United States Patent stergren et al.  
 [ 1 Apr. 29, 1975 STABILIZATION OF METAL CARBONYLS 221 Filed: Apr. 24, 1973 21 Appl. No.: 354,131  
 [30] Foreign Application Priority Data Apr. 25, 1972 Sweden 5416/72 [52] US. Cl. 44/51; 44/67; 44/68; 44/400; 423/417 [51] Int. Cl C101 1/32 [58] Field of Search 44/51, 67, 68; 423/417 [56] References Cited UNITED STATES PATENTS 2,365,377 12/1944 Bell 44/68 X 2,493,714 l/l950 Christ 44/67 2,546,421 3/1951 Bartholomew. 44/68 X 3,018,172 l/l962 Tillman 44/51 Primary E.\&#39;aminer-W. Cannon Attorney, Agent, or Firm-Fisher, Christen &amp; Sabol [57] ABSTRACT A process for stabilizing solutions of metal carbonyls in organic solvents, preferably in hydrocarbons, in which one or more aluminum-containing, organic compounds are dissolved in the solutions as stabilizers. The aluminum in such compounds is directly bonded to carbon and/or oxygen atoms. More specifically, the aluminum containing organic compounds are reaction products between aluminum alkoxides and one or more compounds having the formula:  
 wherein R represents hydrogen, alkyl having up to 8 carbon atoms, aryl or aralkyl having up to 10 carbon atoms, alkoxy having up to 8 carbon atoms, aryloxy or aralkoxy having up to 10 carbon atoms, or a group having the formula:  
 4 Claims, No Drawings STABILIZATION OF METAL CARBONYLS During the last three decades the technical use of metal carbonyls has been of considerable importance within various chemical fields. By metal carbonyls it is here intended compounds of metal atoms and carbon monoxide groups (carbonyl groups), the carbon atoms being linked to the metal atom partly by covalent bonds and partly coordinatively. Several known metal carbonyls constitute complicated cyclic systems, wherein also several different metals can be included and many times linkage conditions difficult to interpret are present. Among the oldest metal carbonyls known, primarily carbonyls of metals in the eighth group of the periodic table, e.g. nickel tetracarbonyl, iron pentacarbonyl and cobalt tetracarbonyl may be mentioned. These three metal carbonyls have a considerable metallurgical importance, as they have such low boiling points that they can be fractioned by distillation, which allows preparation of the respective metals in a chemically pure form. For instance, nickel tetracarbonyl and iron pentacarbonyl have also a great importance as catalysts, as they make possible certain key syntheses, among which, the oxo synthesis and the Reppe synthesis may be mentioned. Also in the motor technology these metal carbonyls have been used sporadically as they have a strong increasing effect on the octane number when added to motor fuels. In this connection, however, the greatest disadvantage of these compounds will appear, namely the instability, which has the effect that no motor fuel so far prepared with them as addition has turned out to be storable. In a dilution of for instance iron pentacarbonyl with gasoline hydrocarbons to a dilution degree as corresponding to an iron content of 0.5 g of iron per litre the originally clear petrol solutions start to become cloudy already after 2 hours due to a separation of gasoline insoluble degradation products of the iron pentacarbonyl, which will gradually be deposited as a thick reddish-brown sediment. This will continue till the remaining gasoline no longer contains any iron in the form of pentacarbonyl and its octane number has reverted to the same value as before the addition of the pentacarbonyl. As light promotes this degradation process the case will be aggravated. These conditions are in a sharp contrast to the properties of a gasoline wherein lead tetraethyl or lead tetramethyl is used as an agent for increasing the octane number.  
  The present invention refers to a method of stabiliz ing solutions of chemically per se very unstable metal carbonyls in gasoline hydrocarbons and especially to prevent a process wherein these metal carbonyls are converted into degradation products which are insoluble in gasoline hydrocarbons and in this way form troublesome suspensions with deposit of a slime-like sediment as a consequence. Of course not only this obviously evident degradation process leads to the fact that the solutions all according to the intended technical objects are no longer useful for purely mechanical reasons or reasons dependent on the consistency, but the degradation of course also has the consequence that the content of the solutions of metal carbonyl which presupposes their technical usefulness for certain objects will rapidly be lower and lower, and in this way they loose their desired technical properties.  
  It has now been found that it is possible to prevent such a degradation process by incorporating in the abovementioned solution separately or in mixtures organic compounds containing aluminum or whose atoms are bonded to carbon atoms or also to oxygen atoms. These organic metal compounds especially consist of reaction products between aluminum alkoxides, which are generally characterized by the formula Al(OR) wherein R represents arbitrary alkyl groups with or without aryl substituents within the carbon chain, preferably then with up to about 10 carbon atoms, and organic compounds, whose functional atom groupings consist of carbonyl groups, either as keto groups in ketones, as aldehyde groups in aldehydes or as esterified carboxyl groups in esters. In the simplest case this means that efficient reaction products according to the invention can be obtained by reacting e.g. acetone with aluminum triethoxide. However, the preparation of aluminum triethoxide involves certain technical difficulties, and therefore aluminum tripropoxide or aluminum tributoxide is preferred. Instead of acetone also ethyl methyl ketone or high-molecular ketones can be used. Diketones are also useful and they are especially advantageous if their carbonyl groups are in the a, &#39;y-positions, as in this case they enclose a so-called acidic methylene group, viz. with two easily displaceable hydrogen atoms, the simplest case being acetylacetone. The ketones can be of a mixed, aliphaticaromatic character so that for instance acetophenone can be used advantageously. it has been found that among the aldehydes, formaldehyde and acetaldehyde are less suitable, but their usefulness increases at larger chain lengths, for instance in propionaldehyde or particularly butyric or isobutyric aldehyde. Still longer chains do not bring any advantages. Also in the case of the aldehydes it should be mentioned that they can also be of an aromatic or mixed aromatic-aliphatic character, which means that benzaldehyde or phenylacetaldehyde are useful. Among the esters the esters of formic acid have appeared to be less advantageous. However, the esters of acetic, propionic or butyric acid can be used advantageously. High molecular esters, however, do not bring any special advantages. It is especially advantageous to use ethyl acetate or methyl acetate. Also aromatic esters, such as phenyl ethyl methylate, cinnamic acid ethyl ester, etc., can be reacted with aluminum alkoxides.  
  Ketocarboxylic acid esters, preferably those wherein the keto group is in the B-position to the esterified carboxyl group, have turned out to be especially suitable for reaction with aluminum alkoxides.  
  Thus, in general the suitable carbonyl compounds can be defined by the formula wherein R represents hydrogen, alkyl with up to 8 carbon atoms, aryl or aralkyl with up to l0 carbon atoms, alkoxy with up to 8 carbon atoms, aryloxy or aralkoxy with up to 10 carbon atoms, or a group having the formula and the groups R R R, and R independently of each other represent hydrogen, alkyl with up to 8 carbon atoms or aryl or aralkyl with up to 10 carbon atoms.  
  According to the invention the aluminum alkoxides can also be reacted with organic compounds, whose functional groups consist of so-called acidic methylene groups, i.e. carbon atoms with movably bonded hydrogen atoms or preferably carbon atoms with a tertiary hydrogen atom, i.e. a hydrogen atom that is bonded to a tertiary carbon atom. It has been found that the amount of metal in the reaction product directly bonded to carbon atoms can be considerably increased with such compounds. These compounds need not contain any functional groups with oxygen atoms but they can consist of hydrocarbons, provided that they contain tertiarily bonded hydrogen atoms. In an especially suitable case triphenylmethane can be used. However, also diphenylethylmethane is advantageous as well as substantially all the compounds, whose general configuration is expressed by the formula T I R (3 R H to be reacted with it need not be stoichiometric. For instance, this means for a simple case, viz. the reaction of aluminum-tributoxide with acetone, where one mole of tributoxide is reacted stoichiometrically with one mole of acetone, the metal entering into an enolic bond with the tautomeric form of the acetone, forming one mole of butanol according to the formula cH (Ii CH3 CH2 All.(OC H aluminum metal in such an amount and at such a form of division in the reaction vessel that an optimally large contact surface between the metal and the liquid reaction compound can be maintained during the course of the reaction. In respect of the most practical embodiment this means that the metal is present in the reaction vessel in the form of a loose layer of metal particles, whose particle size should be between about 0.5 and 5, preferably then between 0.5 and 2 mm in diameter, i.e. in the form of grains. A still less particle size results in that it will be difficult to control the process due to it being highly exothermic. An optical contact surface between the metal and the liquid reaction compound is preferably secured by the layer of solid metal reaching the highest liquid level of the reaction compound in the course of the process. These conditions in the reaction vessel require that the metal surface being in reaction contact with the reaction compound in the reaction process does not undergo any considerable reduction on a percentage basis. In most cases a colloidal metal suspension is formed which together with an increasing porosity of the surface of the metal particles does not only compensate the surface loss due to the relatively small part of metal disappearing through the reaction but also causes an enlargement of the total activated metal surface.  
  Stabilizing systems prepared according to the above description are incorporated into gasoline solutions of metal carbonyls, preferably then metal carbonyls of metals included in group 8 of the periodic table. It is suitable to choose such concentrations in the first step of the mixing process that the carbonyls are not combined in a too diluted state with the aluminum compounds of the stabilizing system, this for reactionkinetical reasons. For instance it has appeared to be suitable to prepare standard stock solutions, wherein the metal carbonyls are present in an amount of 20 volume percent, the amount of organically bonded aluminum metal being about 5-30 grams of metal per litre of standard stock solution. However, this does not principally mean any restriction of the concentration conditions of the stock solutions. As such standard stock solutions can be stored for practically unlimited time without the carbonyls showing any indications of de- C l-l compound A that it has been found to be much more advantageous to use instead a ratio that is less than 1:1, as the compound A in the formula above in the process for the preparation of the stabilizers according to the present invention regarding temperature and pressure conditions and primarily as the reaction products are in contact with an optimally large metal surface, reacts with itself to form more complicatedly built reaction products, the structure of which unknown to a large extent. Among these products are also present real&#34; organometalic compounds with metal-carbon bonds. These secondary processes proceed under additional regeneration of the original butanol, which therefore will be available for reaction of additional amounts of aluminum.  
  The reaction is carried out at temperatures between 80 and 300C, preferably between 120 and 200C, at a normal or elevated pressure and in the presence of composition, they can be considered as an advantageous way of storing the metal carbonyls from a dosage point of view.  
  For a ready to use gasoline, whose octane number has been increased by addition of a metal carbonyl, it has been found that a suitable stabilizing amount of the present stabilizing system consists of one corresponding to 1 part by weight of aluminum to 50-100 parts by weight of the metal in the added metal carbonyl. Greater additions are also effective, but are economically less suitable. Smaller additions will also provide a stabilizing effect, but it is clear that this effect is reduced with decreasing contents, until it is no longer satisfactory.  
  However, it may occur that an aluminum stabilizing system according to the present invention does not provide any sufficiently long stabilization, especially when the additionally diluted solutions of metal carbonyls in gasoline hydrocarbons, for instance up to a carbonyl metal content of 0.2 to 0.6 gram per litre of gasoline solution, is in contact with iron surfaces, for instance in tanks, barrels etc. It is then possible to incorporate small amounts of gasoline-soluble organic salts of manganese or preferably of cobalt into these diluted readyto-use metal carbonyl solutions, the amount of these metals per litre of diluted, finished gasoline not having to exceed than 0.04 gram of metal. As suitable acids for said metal salts it has been found that both aromatic, aliphatic or naphthenic acids can be used. It has been especially advantageous to use salts of 2-ethylhexane carboxylic acid.  
 EXAMPLE 1 A type of aluminum stabilizer is prepared in the following manner in an apparatus consisting of a 4 litre flask, a reflux cooler with gas discharge and a calibrated feed tunnel. The flask has been charged with 2 kg of aluminum metal in the form of pellets of about 3-8 mm diameter and with 100 ml of n-butanol.  
  The flask is heated to about 80C, at which temperature the reaction between the metal and the alcohol starts. The aluminum metal may be activated with iodine. The heat supply is continued until the temperature has reached about 120C. Then the heat supply is discontinued and a continous addition of n-butanol is started. preferably at a rate of l00ml/l0 min. This addition of alcohol is continued until the total amount of alcohol is 2 litres. During this time of addition the temperature of the reaction compound will continue to rise and finally reaches about l35145C Provided that the feeding of the alcohol is controlled at the rate indicated above, a reaction system is present, wherein the reaction product is not dissolved in an excess of n-butanol, but is present in the form of a melt. In this melt there is a certain amount of aluminum suspended colloidally, due to which the aluminum metal surface will be very large. Two litres of n-butanol converts about 196 grams of aluminum into aluminum tributoxide as a melt, wherein aluminum metal moreover is colloidally suspended.  
  lnto this melt at about l35l45C a mixture of 500 ml of acetone and 500 ml of ethyl acetate is continuously fed for 45 min. The reaction now obtained is exothermic, and therefore no rapid decrease of temperature will occur. The end temperature of the reaction mass should not be lower than 1 C. The liquid reaction mass is drained off and diluted with a mixture of hydrocarbons, whose boiling point range corresponds to that of a common car gasoline, so that the total volume of the reaction mass amounts to 4 litres.  
  The solution obtained is here called aluminum stabilizer&#34;. With this aluminum stabilizer, a standard solution of iron pentacarbonyl is prepared by mixing 30 ml of stabilizer, 50 ml of common lead-free car gasoline and ml of iron pentacarbonyl, whereby 100 ml of standard solution of 20 72 of stabilized iron pentacarbonyl is obtained. This standard solution, variant A, has the following quantitative properties:  
  grams lron per 100 ml 8.311 Aluminum 100 ml 0.150  
 Ratio Fe A1 55.4 l  
  The standard solution according to variant A can be stored without any deposition of solid iron-containing decomposition products, such as will take place already after a few hours from a standard solution with the same iron pentacarbonyl content but without addition of organically bonded aluminum and which causes a very rapid decrease of the content of iron in solution.  
  If 6.0 ml of standard solution A is diluted with one litre of common lead-free car gasoline of the octane number 89.1, which means 0.5 gram iron per litre, a car gasoline is obtained having an octane number of 98.3. This diluted gasoline solution can be stored without any deposits of the decomposition products of the iron carbonyl, which would of course cause a very rapid decrease of the octane number.  
  Variant B: An iron pentacarbonyl standard solution of 20 content is prepared by reaction (mixture) of 10 ml of aluminum stabilizer according to this example with 20 ml of iron pentacarbonyl dissolved in ml of common lead-free car gasoline, so that ml of stabilized iron carbonyl solution with the following properties is obtained:  
  grams Content of iron per 100 ml 8.311 aluminum 0.050  
 grams per litre Iron 0.5 Aluminum 0.003 Cobalt 0.020  
 This petrol mixture can be stored without any deposits from decomposition products of iron carbonyl. Nor does the addition of iron or copper filings cause any decomposition of the added iron carbonyl.  
 EXAMPLE 2 1n the same apparatus as described in example 1 half the amount of n-butanol, i.e. 1 litre, is reacted with the same amount of aluminum and under the same temperature conditions as in example 1 thus forming half the amount of aluminum tributoxide. This compound is then reacted with a mixture of 500 m1 of acetone and 500 ml of ethyl acetate under the same temperature conditions. During the addition of these carbonyl compounds, the same progress of temperature is not observed as that under the conditions in example 1, where no additional heat supply was necessary. In example 2 the temperature must be raised to C after adding the carbonyl compound and must be maintained constant for 2 hours, before the reaction product is allowed to cool. Then the cooled reaction liquid is drawn off and diluted with so much of gasoline hydrocarbons that the solution has a volume of 3.2 litres. It can then be reckoned with the same amount of organically bonded aluminum metal per litre as in example 1, which amount usually is about 50 grams per litre of stabilizer. While a molar ratio of hydroxyl keto or carbonyl groups equal to 1.38421 was used in example 1, the ratio in this example is 0.692 1. It is evident that the amount of organically bonded aluminum is not proportional to the amount of butyl alcohol originally used calculated as moles of hydroxyl. In a stabilizer according to this example the amount of organically bonded aluminum, i.e. Al metal in an enolate bond and in direct carbon-bonded form, relative to hydroxyl bonded metal must be greater than in example 1.  
  With an aluminum stabilizer according to example 2, two stabilized iron pentacarbonyl standard solutions were also prepared in a way analogous with example 1.  
 EXAMPLE 2. Variant A 30 ml of aluminum stabilizer according to example 2 are dissolved in 50 ml of lead-free car gasoline and this solution is mixed with 20 ml of iron pentacarbonyl so that 100 ml of stabilized standard solution is obtained. 6 ml of this standard solution are diluted with 1 litre of lead-free gasoline. This will give 0.5 grams of iron and 0.150 grams of aluminum per litre of gasoline, and the ratio Fe AI will then be 55.4:1.  
  The storage stability of this mixture is comparable to that of the mixture according to example 1 A.  
 EXAMPLE 2. Variant B This stabilizing standard solution of iron carbonyl is prepared in a way analogous to that described in example 1. The difference is that as cobalt salt cobalt naphthenate with the same metal content is used. The storage stability in the presence of iron or copper filings was also here satisfactory.  
 EXAMPLE 3 In the same apparatus as described in example 1,17 moles l498,6 grams 1836,5 ml)-isoamylalcoho1 (the optically active form) is reacted with the stoichiometric amount of metal in the presence of 2 kg aluminum pellets. As this alcohol reacts more slowly than nbutanol, the addition must be carried out more slowly, preferably 100 ml per min. A constant temperature of about 150C is maintained. After adding all of this amount, a mixture of 500 ml ethyl acetate (=450,5 grams) and 500 ml acetyl acetone (=488 grams) are added. This solution is continued for 2 hours and the temperature is maintained constant at 150C. Then the temperature is raised to 170C and kept constant for 2 hours, after which the mixture is cooled. After draining off the cool reaction mass, it is diluted with so much lead-free car gasoline that the volume amounts to 3,500 ml. The amount of organically bonded aluminum is found to be 50 grams per litre.  
  From this stabilizing solution, two stabilized iron pentacarbonyl solutions were again prepared as standard solutions with 8.31 1 grams of iron per ml of standard solution, corresponding to an iron pentacarbonyl content of 20 What is claimed is:  
  1. A process for stabilizing a solution of carbonyls of metals of Group VIII of the periodic system in liquid hydrocarbons which comprises dissolving in said solution stabilizing amounts of one or more aluminumcontaining organic compounds, the aluminum in said aluminum-containing organic compound being directly bonded to carbon atoms, oxygen atoms or both, and said aluminum-containing organic compound being the reaction product of at least one aluminum alkoxide and one or more compounds having the formula:  
 l n l 3 and each of the groups R R R and R independently of each other, is hydrogen, alkyl having up to 8 carbon atoms, aryl having up to -10 carbon atoms or aralkyl having up to 10 carbon atoms.  
  2. The process of claim 1 wherein the alkoxy group in the aluminum alkoxide contains no more than 10 carbon atoms.  
  3. The process of claim 1 wherein the aluminumcontaining organic compounds are added to the solutions of metal carbonyls in an amount corresponding to 1 part by weight of aluminum to 50 to 200 parts by weight of the metal in the metal carbonyl.  
 4. The process of claim 1 wherein a carboxylic acid salt of manganese or cobalt is also added to the solu-- tions of the metal carbonyls in an amount corresponding to a maximum amount about 0.04 gram of metal per liter of solution.