Serialize List as JSON

You can use Newtonsoft and dictionary:

    var dict = new Dictionary<int, string>();
    dict.Add(1, "one");
    dict.Add(2, "two");

    var output = Newtonsoft.Json.JsonConvert.SerializeObject(dict);

The output is :

{"1":"one","2":"two"}

Edit

Thanks to @Sergey Berezovskiy for the information.

You are currently using Newtonsoft, so just change your List<KeyValuePair<object, object>> to Dictionary<object,object> and use the serialize and deserialize method from the package.