Monofunctional diferrocenyl compounds
United States Patent 1191 Moffett, Jr. et al 260/439 CY Nielsen Apr. 15, 1975 [5 MONOFUNCTIONAL DIFERRQ&#39;CENYL 3,598,850 8/1971 Dewey 260/439 CY COMPOUNDS [75] Inventor? Arnold T. Nielsen, China Lake, Primary Examiner Leland Sebastian Cahf Attorney, Agent, or Firm-TR. S. Sciascia; Roy Miller; [73] Assignee: The United States of America as Lloyd 5 Pohl represented by the Seeretary of the Navy, Washington, 11C. 1  
 [22] Filed: Mar. 27, 1972 [57] ABSTRACT [21] Appl. No.: 238,583  
  4,4-D1ferr0cenyl-l-pentanol and 3,3-d1ferrocenylbutyl isocyanate are prepared. The compounds are oxida- [52] US. Cl. 260/439 CY; 149/192 tion resistant and can readily be chemicauy attached [51] lilt- C]. C07f 15/02 to Solid rocket propellant binders f use as i [58] Field of Search 260/439 CY rate modifiers [56] References Cited 4 Claims, No Drawings MONOFUNCTIONAL.DIFERROCENYL COMPOUNDS 7 BACKGROUNDOF THE INVENTION 1, Field of&#39;the Invention This invention relates to diferrocenyl compounds and to ,rnethods for; their preparation. More, particularly, this invention .relatesto compounds which contain a reactive moiety andin; which two ferrocenyl groups are attached to a single&#34; carbon atom in a hydrocarbon chainand, completely replace all hydrogen atoms previously attached to that carbon atom.  
  2. Description of the Prior Art Iron containing compounds have long been known to act as burning-rate accelerators when admixed with solid rocket propellants. Examples of those used in the prior an include iron oxide, ferrocene, 1,3-diferrocenyl-&#39; l -butene, 2,2-bis(ethylferrocenyl)propane and others. Each of these materials, when used as a burningrate accelerator, has one ormore disadvantages selected from a list including 1. Low solubility in the propellant. Large particle size reduces effective concentration.  
 2. Inhomogeneityf&#39; 3. Migration within the propellant.  
 I 4. Oxidation sensitivity.  
 5. Volatility.  
 6. Crystallizability of solid additives.  
  Almost all of the above disadvantages cause degradation ofv the propellant and some cause degradation of the liner as well. Some cause erratic burning because during storage, they cause the burning characteristics of the propellant to change.  
  Because of the disadvantages exhibited by previously used iron containing burning-rate accelerators, a considerable amount of research directed toward the prep aration of new iron containing compounds which do not have the above disadvantages has been conducted during the past few years. Much of this work has been directed toward the synthesis of ferrocenyl-substituted compounds.  
  In order to be useful as a burning-rate catalyst, a ferrocenyl-substituted compound should have a highly reactive functional group to permit ready chemical attachment to propellant binders in order to prevent migration. It should have high iron content per functional group. It should be highly resistant to oxidation. It should be highly soluble in hydrocarbon solvents. And it should be readily prepared from ferrocene or inexpensive derivatives.  
 SUMMARY OF THE INVENTION per functional group. The&#39;presence of two ferrocenyl groups on the same. carbon atom having no hydrogen causes the compounds to be highly resistant to oxidation. The compounds are solublein hydrocarbon solvents. And, the compounds are, as will be seen from the description of the preferred embodiment, easily prepared from ferrocene and other readily available chemicals.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Methyl 4,4-diferrocenylpentanoate is a convenient intermediate compound from which the hereinafter claimed compounds can be prepared. Thefollowing examples describe the preparation of methyl 4,4-diferrocenylpentanoate and subsequent reactions leading to the preparation of the claimed compounds, namely, 4,4-diferrocenyl-l-pentanol and 3,3-diferrocenylbutyl isocyanate. All temperatures in the following examples are degrees centigrade.  
 EXAMPLE 1 Methyl 4,4-Diferrocenylpentanoate Polyphosphoric acid was prepared by slowly adding phosphoric anhydride (125 g) to percent phosphoric acid g), followed by warming on a steam bath, with stirring, to obtain a solution. Methanol ml) was added dropwise, with stirring, to the cooled acid and ml of cyclohexane contained in a 3- necked flask equipped with a constant-rate addition funnel, condenser, stirrer, thermometer and nitrogen inlet, keeping the temperature below 60. Ferrocene (93.0 g, 0.5 mole) was introduced into the flask all at once and the stirred mixture heated in an oil bath maintained at 98-100 throughout the reaction. Methyl levulinate (97.5 g, 0.75 mole) was added dropwise with vigorous stirring during 24 hr; about 0.2 mole was added during the first 2 hr and the remainder at a constant rate until all added; temperature 7678 within the mixture throughout the reaction. After cooling to 25, the mixture was stirred with 100 ml each of water and benzene. The deep-orange upper layer was separated from the dark-green lower layer which was extracted twice with benzene. The combined organic solutions were washed successively with water, 10 percent aqueous sodium hydroxide solution and water and dried. Concentration under reduced pressure on a steam bath gave 1 19.1 g of a mixture of oil and crystals. The mixture was heated for 2 hr (ll5130; 1 mm.) in a rotary evaporator provided with a 20 X 3 cm. collection trap. The sublimate was washed thoroughly with water to yield recovered ferrocene (37.6 g, 40.5  
 percent recovery). The residue, a red grease (69.4 g), was distilled under nitrogen through a short still head (Woods metal bath at 250260) to yield at about 0.1 mm. fractions of (1) bp l30-200, 2.2 g, mainly methyl 4-ferrocenylpentanoate (about 1 percent yield); (2) bp 225-236, 48.4. g (40 percent conversion, 67 percent yield based on recovered ferrocene) of methyl 4,4-diferrocenylpentanoate which crystallized on standing, mp l04l07, (3) 16.8 g of black, brittle solid residue. Crystallization of fraction (2) from hexane gave orange-yellow needles, mp l07108; v (KBr) 1725 cm&#34; (C=O); nmr (CDClg) 84.08 (s, 18, FcH), 3.63 (s, 3, CH O), 2.22 (s, 4, CH CH 1.62 (s, 3, CH C); elemental analyses below. The undistilled crude ester crystallized with difficulty from hexane; it could be purified by dry-column chromatography on alumina (benzene).  
  Anal. Calcd. for C H Fe O C, 64.50; H, 5.83; Fe, 23.07; Mol wt 484.2. Found: C, 64.74; H, 6.00; Fe, 23.29; Mol wt 500 (osmometry, CHCl Ferrocene could be recovered from the dark-green aqueous acid solutions by treatment with reducing agents such as sodium sulfite or ascorbic acid. Recov ery yields were 0.1-4 percent. Only trace amounts of ferrocene were recovered by this treatment following the reaction procedure described above. Larger amounts (2-4 percent) were obtained when sulfuric acid was the catalyst or when methyl levulinate was added rapidly to the reaction mixture.  
 EXAMPLE 2 4,4-Diferrocenyl-1-pentanol A solution of methyl 4,4-diferrocenyl-pentanoate (3.4 g, 0.007 mole) in ml of dry tetrahydrofuran was added dropwise with stirring during 15 min to a solution of 0.27 g (0.007 mole) of lithium aluminum hydride in 25 ml of ether. The mixture was heated under reflux with stirring for 80 min. The mixture was chilled in an ice bath and stirred with an excess of N hydrochloric acid until all aluminum salts were dissolved. The ether layer was separated, washed with water and dried. Concentration under reduced pressure gave 3.0 g (94 percent yield) of the alcohol, mp l0411l; recrystallization from cyclohexane gave small prisms, 2.8 g, mp l10l1l; recrystallization from benzene gave chunky prisms, mp 1l5116; v (KBr) 3350 cm (OH), carbonyl bands absent; nmr (CDCl-,,) 6 4.12 (s, 18, FcH), 3.33.8(m,2,CH), l.2-2.2[m,4,(CH 1.65 (s, 3, CH 1.40 (s,1,0H).  
 Anal. Calcd. for C l-l Fe O: C, 65.82; H, 6.19; Fe,  
 EXAMPLE 3 4,4-Differrocenylpentanoic Acid,-- A mixture of methyl 4,4-diferrocenyl-pentanoate (24.2 g, 0.05  
 mole) and potassium hydroxide (15 g, 85 percent assay) dissolved in a solution of 50 ml each of water, ethanol and dioxane was heated on the steam bath (nitrogen atmosphere) for 3 hr. The solution was concentrated to remove solvents; 50 ml of water and 100 ml of dioxane were added and the mixture warmed to dissolve the product. The cooled solution was acidified to pH 1 by addition of concentrated hydrochloric acid; the mixture was then warmed on the steam bath to dissolve all organic material. The solution was concentrated under reduced pressure on a steam bath to remove solvents and the residue treated with 500 ml of water; the solid was filtered and washed thoroughly with water. The dried solid was heated in boiling benzene (300 ml) to dissolve organic material and filtered hot to remove insoluble matter. The filtrate was concentrated to dryness and finally heated on the steam bath at 0.1 mm. for 2 hours to yield 23.3 g (99 percent) of the acid, mp l94-199; recrystallization from cyclohexane gave prisms, mp 195l99; it is necessary to heat at 100, 0.1 mm., for 2 hours to remove all cyclohexane solvent; v (KBr) 1690 cm (C=O); nmr (CDCl 83.98 (s, 18, FcH), 2.20 (s, 4, CH CH 1.55 (s, 3, CH  
  Anal. Calcd. for c u-n re o ac, 63.89; H, 5.57; Fe, 23.75; Mol wt 470.2 Found: C, 64.05; H, 5.65; Fe, 23.72; Mol wt 481 (osmometry, CHCl EXAMPLE 4 4,4-Diferrocenylpentanoyl chloride 4,4-Diferrocenylpentanoic acid (23.5 g, 0.05 mole) dissolved in 500 ml of dry benzene and pyridine (4.8 g, 0.06 mole) was treated with phosphorus trichloride (8.2 g, 0.06 mole). The mixture was heated in a nitrogen atmosphere on a steam bath from 25 to reflux during 15 min and at reflux for 30 min. The mixture was cooled to room temperature and the supernatent solution filtered using a Buchner funnel to separate it from insoluble material adhering to the flask; the solid residue was rinsed twice with dry benzene. The combined benzene solutions were concentrated under reduced pressure, care being taken not to heat the flask contents above 25. [CAUTlONl The acid chloride decomposes rapidly, evolving hydrogen chloride, when heated at -l00.] The crude oily acid chloride revealed a strong carbonyl band at 1,795 cm and no other carbonyl absorption bands; yield 23.7 g (97 percent). The crude acid chloride was used immediately, without further treatment, for conversion to the acyl azide described below.  
  Prolonging the reaction time in refluxing benzene beyond 45 min to 2-6 hr resulted in lowered yields of the acid chloride and formation of much benzene-insoluble material, as well as a carbonyl-containing impurity in the product (v 1,670 cm). Heating the crude, neat acid chloride on the steam bath for a few minutes resulted in rapid evolution of hydrogen chloride and formation of a black brittle solid having no acid chloride carbonyl absorption at 1,795 cm and only a single sharp carbonyl band at 1,670 cm (hydroxyl absorption absent). Attempts to purify the crude acid chloride in benzene solution by washing with cold saturated sodium bicarbonate solution caused partial hydrolysis to the acid salt; severe ernulsification resulted making the extraction quite difficult.  
 EXAMPLE 5 4,4-Diferrocenylpentanoyl Azide 4,4-Diferrocenylpentanoyl chloride (24.4 g, about 0.05 mole) of crude material prepared as described above was dissolved in 100 ml of dry tetrahydrofuran and added dropwise with stirring to a solution of sodium azide (4.55 g, 0.07 mole) in 15 ml of water chilled to 3 in an ice bath, keeping the temperature below 5 during the addition (nitrogen atmosphere). Stirring was continued for 30 min at 34. The infrared spectrum of an aliquot sample showed strong bands at 1,710 cm (C=O) and 2,130 cm (N characteristic of the acyl azide, and virtually no other components as indicated by the absence of other infrared bands, including those of the acid chloride or carboxylic acid. A trace of isocyanate was indicated by extremely weak absorption at 2,270 cm&#34;. The mixture was concentrated under reduced pressure at 25 to remove tetrahydrofuran and the gummy residue diluted with 30 ml of water. The following operations were performed as rapidly as possible due to the short half-life of the acyl azide. Benzene (500 ml) was added to dissolve most of the residue; some gummy solid remained undissolved in either the benzene or water phase. The aqueous layer containing some benzene (emulsion) was separated and mixed with diatomaceous silica (Celite) and filtered. The filtrate was added to the benzene layer and the combined benzene solutions extracted twice with cold water and cold 10 percent aqueous sodium hydroxide solution. More insoluble gummy sodium salt precipitated. Diatomaceous silica was added to the aqueous layer containing the precipitate and the mixture filtered through a Buchner funnel. The aqueous layer was separated from the filtrate and the combined benzene layers washed with water and dried with magnesium sulfate for about one hour. The solution was filtered and concentrated under reduced pressure at 25 to remove benzene leaving the crude acyl azide as a gummy solid, 19.8 g (85 percent); 11 (film) 1,710 (C=O), 2,130 cm (N The crude azide was employed immediately for conversion into the corresponding isocyanate.  
 EXAMPLE 6 3,3-Diferrocenylbutyl isocyanate.  
  The crude acyl azide prepared above was dissolved in 400 ml of dry benzene and stored over molecular sieves for 16 hr at 25 in a flask having a calcium chloride tube attached. Nitrogen gas evolved slowly during this time; the reaction was completed by heating the solution under reflux for 0.5 hr. The benzene was removed under reduced pressure at 25 to yield 19.1 g of crude isocyanate as orange crystals, mp 132135; extraction with 500 ml of dry, refluxing cyclohexane, followed by cooling, filtration of insoluble material, and concentration of the filtrate gave the isocyanate as orange crystals; 17.0 g (90 percent; 74 percent from the ester), mp 135-l37 11(KBr) 2,270 cm (NCO): nmr (CDCl:,) 8 3.92 (s, 18, Fcl-l), 1.8-3.3 (complex A B multiplet centered at 2.1 and 3.1,4, CH CH 1.54 (s,&#39;3, CH  
  Anal. Calcd. for C H Fe NO: C, 64.27; H, 5.39; Fe, 23.91; N, 3.00; M01 wt 467.2. Found: C, 64.03; H, 5.47; Fe, 24.07; N, 2.96; M01 wt, 470 (osmometry, CHCl The compounds, 4,4-diferrocenyl-l-pentanol and 3,3-diferrocenylbutyl isocyanate, are especially useful as burning-rate catalysts for solid rocket propellants for several reasons. Firstly, the functional group of either compound (hydroxy or isocyanate) is reactive with functional groups of materials commonly used in solid rocket propellants. This permits the compounds to be chemically combined with solid rocket propellants to prevent migration. Secondly, the compounds have high iron content per functional group (two iron atoms per hydroxy or isocyanate). Thirdly, the presence of two ferrocenyl groups on a single carbon atom and the absence of any hydrogen atoms on that carbon atom renders the compounds highly resistant to oxidation. Fourthly, the compounds are soluble in commonly used organic solvents. This permits them to be easily incorporated into propellant mixes. Finally, as can be seen from the above examples, the compounds are easily prepared from readily available starting materials.  
 I claim:  
 1. 4,4-Diferrocenyl-l -pentanol.  
 2. 3,3-Diferrocenylbutyl isocyanate.  
 3. A method for preparing 4,4-diferrocenyl-lpentanol comprising the steps of:  
 a. reacting methyl levulinate with ferrocene in the presence of a polyphosphoric acid catalyst and a methanol-cyclohexane solvent held at a temperature of from 76 to 78 C to produce methyl 4,4-diferrocenylpentanoate;  
 b. separating 4,4-diferrocenylpentanoate from side products obtained from the reaction in step (a); and  
 c. reacting methyl 4,4-diferrocenyl-pentanoate with lithium aluminum hydride by adding a solution of methyl 4,4-diferrocenylpentanoate in tetrahydrofuran to a solution of lithium aluminum hydride in ether and refluxing to produce 4,4-diferrocenyl-lpentanol.  
 4. A method for preparing 3,3-diferrocenylbutyl isocyanate comprising the steps of:  
 a. hydrolyzing methyl 4,4-diferrocenylpantanoate with potassium hydroxide to produce 4,4- diferrocenylpantanoic acid;  
 b. reacting 4,4-diferrocenylpentanoic acid with phosphorous trichloride to produce 4,4-diferrocenylpentanoyl chloride;  
 0. reacting 4,4-diferrocenylpentanoyl chloride with sodium azide to produce 4,4-diferrocenylpentanoyl azide; and d. dissolving 4,4-diferrocenylpentanoyl azide in dry benzene and refluxing to produce 3,3-  
 diferrocenylbutyl isocyanate.